Reverts "Enable `onlyUseTipOfTreeTargetsExistenceToFilterTargets`. (#4735)" (#4736)

Reverts: flutter/cocoon#4735
Initiated by: matanlurey
Reason for reverting: Targets are not queueing as expected.
Original PR Author: matanlurey

Reviewed By: {jtmcdole}

This change reverts the following previous change:
Towards https://github.com/flutter/flutter/issues/169625.
diff --git a/app_dart/config.yaml b/app_dart/config.yaml
index 2b52493..02b9992 100644
--- a/app_dart/config.yaml
+++ b/app_dart/config.yaml
@@ -6,7 +6,7 @@
 backfillerCommitLimit: 50
 
 ciYaml:
-  onlyUseTipOfTreeTargetsExistenceToFilterTargets: true
+  onlyUseTipOfTreeTargetsExistenceToFilterTargets: false
 
 contentAwareHashing:
   # This will cause PRs that enter the merge queue to wait on CAH hashing