Reverts "Manually bump Dart to 3.4.0-34.0.dev" (flutter#49802)

Reverts flutter#49792
Initiated by: zanderso
This change reverts the following previous change:
Original Description:
https://dart.googlesource.com/sdk.git/+log/d6c08fa9bb54..992d6c2562

DEPS

@@ -65,7 +65,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/main/DEPS
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '992d6c2562abddf06306226301a4cdefee63513f',
+  'dart_revision': 'd6c08fa9bb54dfc52e32ee879ae157f8a01d5a50',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py

ci/licenses_golden/licenses_dart

@@ -1,4 +1,4 @@
-Signature: 9719d8ff58c1aefff3edea64966c868f
+Signature: 60ebc270fcd5313847ed98c6ce909e6a
 
 ====================================================================================================
 LIBRARY: dart
@@ -4707,7 +4707,7 @@ Exhibit B - "Incompatible With Secondary Licenses" Notice
   This Source Code Form is "Incompatible With Secondary Licenses", as
   defined by the Mozilla Public License, v. 2.0.
 
-You may obtain a copy of this library's Source Code Form from: https://dart.googlesource.com/sdk/+/992d6c2562abddf06306226301a4cdefee63513f
+You may obtain a copy of this library's Source Code Form from: https://dart.googlesource.com/sdk/+/d6c08fa9bb54dfc52e32ee879ae157f8a01d5a50
 /third_party/fallback_root_certificates/
 
 ====================================================================================================