remove an unused flutter run flag (#17667)

packages/flutter_tools/lib/src/commands/run.dart

diff --git a/packages/flutter_tools/lib/src/commands/run.dart b/packages/flutter_tools/lib/src/commands/run.dart
index d8e8952..7a21158 100644
--- a/packages/flutter_tools/lib/src/commands/run.dart
+++ b/packages/flutter_tools/lib/src/commands/run.dart
@@ -83,10 +83,6 @@
     requiresPubspecYaml();
 
     argParser
-      ..addFlag('full-restart',
-        defaultsTo: true,
-        help: 'Stop any currently running application process before running the app.',
-      )
       ..addFlag('start-paused',
         negatable: false,
         help: 'Start in a paused mode and wait for a debugger to connect.',