cleanup patch generation to preseve comments and remove @patch

test/dart_codegen/expect/async/schedule_microtask.dart

Index: test/dart_codegen/expect/async/schedule_microtask.dart
diff --git a/test/dart_codegen/expect/async/schedule_microtask.dart b/test/dart_codegen/expect/async/schedule_microtask.dart
index 3dd202a9240b3aafe69422ea7af6ceeb4d91a3e7..11b4b2783912e13800dc6dd12100d466ad4c6338 100644
--- a/test/dart_codegen/expect/async/schedule_microtask.dart
+++ b/test/dart_codegen/expect/async/schedule_microtask.dart
@@ -70,7 +70,7 @@ void scheduleMicrotask(void callback()) {
       .scheduleMicrotask(Zone.current.bindCallback(callback, runGuarded: true));
 }
 class _AsyncRun {
-  @patch static void _scheduleImmediate(void callback()) {
+  static void _scheduleImmediate(void callback()) {
     scheduleImmediateClosure(callback);
   }
 }