Revert two Kernel changes that were causing test failures.

tests/language/async_star_regression_2238_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // This is a regression test for issue 2238
 import "dart:async";
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 main() {
   f() async* {
     label1:
     label2:
     yield 0;
   }
 
   asyncStart();
   f().toList().then((list) {
     Expect.listEquals([0], list);
     asyncEnd();
   });
 }