cleanup patch generation to preseve comments and remove @patch

test/dart_codegen/expect/async/deferred_load.dart

Index: test/dart_codegen/expect/async/deferred_load.dart
diff --git a/test/dart_codegen/expect/async/deferred_load.dart b/test/dart_codegen/expect/async/deferred_load.dart
index 869bbfe5ac645918feab0b72bb9c594ee252ff57..a6624a58ef0db0429cc94b86215046b34c2f808f 100644
--- a/test/dart_codegen/expect/async/deferred_load.dart
+++ b/test/dart_codegen/expect/async/deferred_load.dart
@@ -5,7 +5,7 @@ class DeferredLibrary {
   final String libraryName;
   final String uri;
   const DeferredLibrary(this.libraryName, {this.uri});
-  @patch Future<Null> load() {
+  Future<Null> load() {
     throw 'DeferredLibrary not supported. ' 'please use the `import "lib.dart" deferred as lib` syntax.';
   }
 }