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

sdk/lib/_internal/pub_generated/test/run/allows_dart_extension_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 '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 const SCRIPT = """
 import 'dart:io';
 
 main() {
   stdout.writeln("stdout output");
   stderr.writeln("stderr output");
   exitCode = 123;
 }
 """;
 
 main() {
   initConfig();
   integration('allows a ".dart" extension on the argument', () {
-    d.dir(appPath, [
-      d.appPubspec(),
-      d.dir("bin", [
-        d.file("script.dart", SCRIPT)
-      ])
-    ]).create();
+    d.dir(
+        appPath,
+        [d.appPubspec(), d.dir("bin", [d.file("script.dart", SCRIPT)])]).create();
 
     var pub = pubRun(args: ["script.dart"]);
     pub.stdout.expect("stdout output");
     pub.stderr.expect("stderr output");
     pub.shouldExit(123);
   });
 }