Revert "Use native async/await support in pub."

sdk/lib/_internal/pub_generated/test/run/nonexistent_dependency_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.
 
 import '../../lib/src/exit_codes.dart' as exit_codes;
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
   integration('Errors if the script is in an unknown package.', () {
-    d.dir(appPath, [
-      d.appPubspec()
-    ]).create();
+    d.dir(appPath, [d.appPubspec()]).create();
 
     var pub = pubRun(args: ["foo:script"]);
-    pub.stderr.expect('Could not find package "foo". Did you forget to add a '
-        'dependency?');
+    pub.stderr.expect(
+        'Could not find package "foo". Did you forget to add a ' 'dependency?');
     pub.shouldExit(exit_codes.DATA);
   });
 }