Delete legacy flow for closeMqGuardAfterPresubmit == false (#5101)

Deleting legacy `closeMqGuardAfterPresubmit = false` flow as it obsolete

**Context:**
We have 2  different processing flows based on whether `processJobStatusUpdate` config variable is `true` or `false`:

1. **Legacy**. if `closeMqGuardAfterPresubmit` flag is set to `false` then flow is the following: 

```mermaid
sequenceDiagram
    LUCI->>Cocoon: Build complete<br/>notification
    Cocoon->>Github: Update Check
    Github->>Cocoon: Check complete<br/>notification
    Note over Cocoon: Check complete processing
    Cocoon->>Github: If all success<br/>unlock merge queue
```

For **Check complete processing** `processJobStatusUpdate()` called with `PresubmitJobState` constructed from check using `PresubmitJobState.fromCheckRun()` 

2. **Current**.  if `closeMqGuardAfterPresubmit` flag is set to `true` or for **Unified Check Run** flow :

```mermaid
sequenceDiagram
    LUCI->>Cocoon: Build complete<br/>notification
    Note over Cocoon: Build complete processing
    Cocoon->>Github: Update Check<br/>or Job in firestore
    Cocoon->>Github: If all success<br/>unlock merge queue
    Github->>Cocoon: Check complete<br/>notification
    Note over Cocoon: Ignoring
```
diff --git a/app_dart/lib/src/model/common/presubmit_completed_check.dart b/app_dart/lib/src/model/common/presubmit_completed_check.dart
index 6aba3c4..6de08aa 100644
--- a/app_dart/lib/src/model/common/presubmit_completed_check.dart
+++ b/app_dart/lib/src/model/common/presubmit_completed_check.dart
@@ -64,30 +64,6 @@
     this.buildId,
   });
 
-  /// Creates a [PresubmitCompletedJob] from a GitHub [CheckRun].
-  factory PresubmitCompletedJob.fromCheckRun(
-    cocoon_checks.CheckRun checkRun,
-    RepositorySlug slug,
-  ) {
-    return PresubmitCompletedJob(
-      name: checkRun.name!,
-      sha: checkRun.headSha!,
-      slug: slug,
-      status: ChecksExtension.fromConclusion(checkRun.conclusion),
-      isMergeGroup: _isMergeGroup(checkRun.checkSuite?.headBranch),
-      checkRunId: checkRun.id!,
-      checkSuiteId: checkRun.checkSuite?.id,
-      headBranch: checkRun.checkSuite?.headBranch,
-      isUnifiedCheckRun: false,
-      // CheckRun model doesn't have time/summary fields currently
-      startTime: null,
-      endTime: null,
-      summary: null,
-      buildNumber: null,
-      buildId: null,
-    );
-  }
-
   /// Creates a [PresubmitCompletedJob] from a BuildBucket [Build].
   factory PresubmitCompletedJob.fromBuild(
     Build build,
diff --git a/app_dart/lib/src/request_handlers/presubmit_luci_subscription.dart b/app_dart/lib/src/request_handlers/presubmit_luci_subscription.dart
index 5878d32..8a96afc 100644
--- a/app_dart/lib/src/request_handlers/presubmit_luci_subscription.dart
+++ b/app_dart/lib/src/request_handlers/presubmit_luci_subscription.dart
@@ -165,16 +165,12 @@
       );
     }
     if (!rescheduled) {
-      // Process to the check-run status in the merge queue document during
-      // the LUCI callback.
-      if (config.flags.closeMqGuardAfterPresubmit || isUnifiedCheckRun) {
-        final check = PresubmitCompletedJob.fromBuild(
-          build,
-          userData,
-          status: override == .neutral ? .neutral : null,
-        );
-        await _scheduler.processCheckRunCompleted(check);
-      }
+      final check = PresubmitCompletedJob.fromBuild(
+        build,
+        userData,
+        status: override == .neutral ? .neutral : null,
+      );
+      await _scheduler.processCheckRunCompleted(check);
     }
 
     return Response.emptyOk;
diff --git a/app_dart/lib/src/service/scheduler.dart b/app_dart/lib/src/service/scheduler.dart
index ced9831..6a712a3 100644
--- a/app_dart/lib/src/service/scheduler.dart
+++ b/app_dart/lib/src/service/scheduler.dart
@@ -1625,14 +1625,7 @@
   ) async {
     switch (checkRunEvent.action) {
       case 'completed':
-        if (!_config.flags.closeMqGuardAfterPresubmit) {
-          await processCheckRunCompleted(
-            PresubmitCompletedJob.fromCheckRun(
-              checkRunEvent.checkRun!,
-              checkRunEvent.repository!.slug(),
-            ),
-          );
-        }
+        // Processing of completed check runs is moved to PresubmitLuciSubscription.
         break;
       case 'rerequested':
         return await _reRun(checkRunEvent);
diff --git a/app_dart/test/model/common/presubmit_completed_check_test.dart b/app_dart/test/model/common/presubmit_completed_check_test.dart
index 79f2ca5..d2fdc37 100644
--- a/app_dart/test/model/common/presubmit_completed_check_test.dart
+++ b/app_dart/test/model/common/presubmit_completed_check_test.dart
@@ -8,7 +8,6 @@
 import 'package:cocoon_service/src/model/commit_ref.dart';
 import 'package:cocoon_service/src/model/common/presubmit_completed_check.dart';
 import 'package:cocoon_service/src/model/firestore/base.dart';
-import 'package:cocoon_service/src/model/github/checks.dart' as cocoon_checks;
 import 'package:cocoon_service/src/service/config.dart';
 import 'package:cocoon_service/src/service/luci_build_service/user_data.dart';
 import 'package:fixnum/fixnum.dart';
@@ -22,28 +21,6 @@
     const sha = 'abc';
     final slug = RepositorySlug('flutter', 'flutter');
 
-    test('fromCheckRun creates correct instance', () {
-      final checkRun = const cocoon_checks.CheckRun(
-        id: 1,
-        name: 'test_check',
-        headSha: sha,
-        conclusion: 'success',
-      );
-
-      final check = PresubmitCompletedJob.fromCheckRun(checkRun, slug);
-
-      expect(check.name, 'test_check');
-      expect(check.sha, sha);
-      expect(check.slug, slug);
-      expect(check.status, TaskStatus.succeeded);
-      expect(check.isMergeGroup, false);
-      expect(check.checkRunId, 1);
-      expect(check.checkSuiteId, null);
-      expect(check.headBranch, null);
-      expect(check.isUnifiedCheckRun, false);
-      expect(check.checkRun.name, 'test_check');
-    });
-
     test('fromBuild creates correct unified check', () {
       final build = Build(
         id: Int64.MAX_VALUE,
diff --git a/app_dart/test/request_handlers/presubmit_luci_subscription_neutral_test.dart b/app_dart/test/request_handlers/presubmit_luci_subscription_neutral_test.dart
index 1dfae51..1745802 100644
--- a/app_dart/test/request_handlers/presubmit_luci_subscription_neutral_test.dart
+++ b/app_dart/test/request_handlers/presubmit_luci_subscription_neutral_test.dart
@@ -35,11 +35,7 @@
   setUp(() async {
     firestore = FakeFirestoreService();
 
-    config = FakeConfig(
-      dynamicConfig: DynamicConfig.fromJson({
-        'closeMqGuardAfterPresubmit': true,
-      }),
-    );
+    config = FakeConfig();
     mockGithubChecksService = MockGithubChecksService();
     mockScheduler = MockScheduler();
 
diff --git a/app_dart/test/request_handlers/presubmit_luci_subscription_test.dart b/app_dart/test/request_handlers/presubmit_luci_subscription_test.dart
index 54f1bb0..b5a25fd 100644
--- a/app_dart/test/request_handlers/presubmit_luci_subscription_test.dart
+++ b/app_dart/test/request_handlers/presubmit_luci_subscription_test.dart
@@ -39,11 +39,7 @@
   setUp(() async {
     firestore = FakeFirestoreService();
 
-    config = FakeConfig(
-      dynamicConfig: DynamicConfig.fromJson({
-        'closeMqGuardAfterPresubmit': true,
-      }),
-    );
+    config = FakeConfig();
     mockLuciBuildService = MockLuciBuildService();
     mockGithubChecksService = MockGithubChecksService();
     mockScheduler = MockScheduler();
diff --git a/app_dart/test/service/scheduler_test.dart b/app_dart/test/service/scheduler_test.dart
index 7f84931..8d801d3 100644
--- a/app_dart/test/service/scheduler_test.dart
+++ b/app_dart/test/service/scheduler_test.dart
@@ -1654,9 +1654,16 @@
               for (final ignored in Scheduler.kCheckRunsToIgnore) {
                 expect(
                   await scheduler.processCheckRunCompleted(
-                    PresubmitCompletedJob.fromCheckRun(
-                      createCocoonCheckRun(name: ignored, sha: 'abc123'),
-                      createGithubRepository().slug(),
+                    PresubmitCompletedJob(
+                      name: ignored,
+                      sha: 'abc123',
+                      slug: createGithubRepository().slug(),
+                      status: TaskStatus.succeeded,
+                      isMergeGroup: false,
+                      checkRunId: 1,
+                      checkSuiteId: 668083231,
+                      headBranch: 'master',
+                      isUnifiedCheckRun: false,
                     ),
                   ),
                   isTrue,
@@ -1689,9 +1696,16 @@
 
             expect(
               await scheduler.processCheckRunCompleted(
-                PresubmitCompletedJob.fromCheckRun(
-                  createCocoonCheckRun(name: 'Bar bar', sha: 'abc123'),
-                  createGithubRepository().slug(),
+                PresubmitCompletedJob(
+                  name: 'Bar bar',
+                  sha: 'abc123',
+                  slug: createGithubRepository().slug(),
+                  status: TaskStatus.succeeded,
+                  isMergeGroup: false,
+                  checkRunId: 1,
+                  checkSuiteId: 668083231,
+                  headBranch: 'master',
+                  isUnifiedCheckRun: false,
                 ),
               ),
               isFalse,
@@ -1728,9 +1742,16 @@
 
             expect(
               await scheduler.processCheckRunCompleted(
-                PresubmitCompletedJob.fromCheckRun(
-                  createCocoonCheckRun(name: 'Bar bar', sha: 'abc123'),
-                  createGithubRepository().slug(),
+                PresubmitCompletedJob(
+                  name: 'Bar bar',
+                  sha: 'abc123',
+                  slug: createGithubRepository().slug(),
+                  status: TaskStatus.succeeded,
+                  isMergeGroup: false,
+                  checkRunId: 1,
+                  checkSuiteId: 668083231,
+                  headBranch: 'master',
+                  isUnifiedCheckRun: false,
                 ),
               ),
               isFalse,
@@ -1782,9 +1803,16 @@
 
               expect(
                 await scheduler.processCheckRunCompleted(
-                  PresubmitCompletedJob.fromCheckRun(
-                    createCocoonCheckRun(name: 'Bar bar', sha: 'abc123'),
-                    createGithubRepository().slug(),
+                  PresubmitCompletedJob(
+                    name: 'Bar bar',
+                    sha: 'abc123',
+                    slug: createGithubRepository().slug(),
+                    status: TaskStatus.succeeded,
+                    isMergeGroup: false,
+                    checkRunId: 1,
+                    checkSuiteId: 668083231,
+                    headBranch: 'master',
+                    isUnifiedCheckRun: false,
                   ),
                 ),
                 isTrue,
@@ -1892,9 +1920,16 @@
 
             expect(
               await scheduler.processCheckRunCompleted(
-                PresubmitCompletedJob.fromCheckRun(
-                  createCocoonCheckRun(name: 'Bar bar', sha: 'testSha'),
-                  createGithubRepository().slug(),
+                PresubmitCompletedJob(
+                  name: 'Bar bar',
+                  sha: 'testSha',
+                  slug: createGithubRepository().slug(),
+                  status: TaskStatus.succeeded,
+                  isMergeGroup: false,
+                  checkRunId: 1,
+                  checkSuiteId: 668083231,
+                  headBranch: 'master',
+                  isUnifiedCheckRun: false,
                 ),
               ),
               isTrue,
@@ -2036,13 +2071,16 @@
 
               expect(
                 await scheduler.processCheckRunCompleted(
-                  PresubmitCompletedJob.fromCheckRun(
-                    createCocoonCheckRun(
-                      name: 'Bar bar',
-                      sha: 'testSha',
-                      checkSuiteId: 0,
-                    ),
-                    createGithubRepository().slug(),
+                  PresubmitCompletedJob(
+                    name: 'Bar bar',
+                    sha: 'testSha',
+                    slug: createGithubRepository().slug(),
+                    status: TaskStatus.succeeded,
+                    isMergeGroup: false,
+                    checkRunId: 1,
+                    checkSuiteId: 0,
+                    headBranch: 'master',
+                    isUnifiedCheckRun: false,
                   ),
                 ),
                 isTrue,
@@ -2145,9 +2183,16 @@
 
             expect(
               await scheduler.processCheckRunCompleted(
-                PresubmitCompletedJob.fromCheckRun(
-                  createCocoonCheckRun(name: 'Bar bar', sha: 'testSha'),
-                  createGithubRepository().slug(),
+                PresubmitCompletedJob(
+                  name: 'Bar bar',
+                  sha: 'testSha',
+                  slug: createGithubRepository().slug(),
+                  status: TaskStatus.succeeded,
+                  isMergeGroup: false,
+                  checkRunId: 1,
+                  checkSuiteId: 668083231,
+                  headBranch: 'master',
+                  isUnifiedCheckRun: false,
                 ),
               ),
               isTrue,
@@ -2409,13 +2454,16 @@
 
               expect(
                 await scheduler.processCheckRunCompleted(
-                  PresubmitCompletedJob.fromCheckRun(
-                    createCocoonCheckRun(
-                      name: 'Bar bar',
-                      sha: 'testSha',
-                      conclusion: 'failure',
-                    ),
-                    createGithubRepository().slug(),
+                  PresubmitCompletedJob(
+                    name: 'Bar bar',
+                    sha: 'testSha',
+                    slug: createGithubRepository().slug(),
+                    status: TaskStatus.failed,
+                    isMergeGroup: false,
+                    checkRunId: 1,
+                    checkSuiteId: 668083231,
+                    headBranch: 'master',
+                    isUnifiedCheckRun: false,
                   ),
                 ),
                 isTrue,
@@ -2492,14 +2540,16 @@
 
               expect(
                 await scheduler.processCheckRunCompleted(
-                  PresubmitCompletedJob.fromCheckRun(
-                    createCocoonCheckRun(
-                      name: 'Bar bar',
-                      sha: 'testSha',
-                      conclusion: 'failure',
-                      headBranch: headBranch,
-                    ),
-                    createGithubRepository().slug(),
+                  PresubmitCompletedJob(
+                    name: 'Bar bar',
+                    sha: 'testSha',
+                    slug: createGithubRepository().slug(),
+                    status: TaskStatus.failed,
+                    isMergeGroup: true,
+                    checkRunId: 1,
+                    checkSuiteId: 668083231,
+                    headBranch: headBranch,
+                    isUnifiedCheckRun: false,
                   ),
                 ),
                 isTrue,
@@ -2575,13 +2625,16 @@
 
             expect(
               await scheduler.processCheckRunCompleted(
-                PresubmitCompletedJob.fromCheckRun(
-                  createCocoonCheckRun(
-                    name: 'Bar bar',
-                    sha: 'testSha',
-                    headBranch: headBranch,
-                  ),
-                  createGithubRepository().slug(),
+                PresubmitCompletedJob(
+                  name: 'Bar bar',
+                  sha: 'testSha',
+                  slug: createGithubRepository().slug(),
+                  status: TaskStatus.succeeded,
+                  isMergeGroup: true,
+                  checkRunId: 1,
+                  checkSuiteId: 668083231,
+                  headBranch: headBranch,
+                  isUnifiedCheckRun: false,
                 ),
               ),
               isTrue,
@@ -2698,9 +2751,16 @@
 
               expect(
                 await scheduler.processCheckRunCompleted(
-                  PresubmitCompletedJob.fromCheckRun(
-                    createCocoonCheckRun(name: 'Bar bar', sha: 'testSha'),
-                    createGithubRepository().slug(),
+                  PresubmitCompletedJob(
+                    name: 'Bar bar',
+                    sha: 'testSha',
+                    slug: createGithubRepository().slug(),
+                    status: TaskStatus.succeeded,
+                    isMergeGroup: false,
+                    checkRunId: 1,
+                    checkSuiteId: 668083231,
+                    headBranch: 'master',
+                    isUnifiedCheckRun: false,
                   ),
                 ),
                 isTrue,