Add missing compile-time errors for async/await.

tests/compiler/dart2js/async_await_syntax_test.dart

 // Copyright (c) 2014, 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.
 
 // Test that dart2js produces the expected static type warnings and
 // compile-time errors for these tests.
 
 import 'frontend_checker.dart';
 
 /// Map of test files to run together with their associated whitelist.
 ///
 /// For instance
 ///     'language/async_await_syntax_test.dart': const ['a03b', 'a04b']
 /// includes the multitest in 'language/async_await_syntax_test.dart' but
 /// expects the subtests 'a03b' and 'a04c' to fail.
 const Map<String, List<String>> TESTS = const <String, List<String>>{
-  'language/async_await_syntax_test.dart': const ['a05h', 'c11a', 'c11b'],
+  'language/async_await_syntax_test.dart': const [],
 };
 
 void main(List<String> arguments) {
-  check(TESTS, arguments: arguments, options: ['--enable-async']);
+  check(TESTS, arguments: arguments, options: []);
 }