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

sdk/lib/_internal/pub_generated/test/global/activate/supports_version_solver_backtracking_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 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
   integration('performs verison solver backtracking if necessary', () {
     servePackages((builder) {
       builder.serve("foo", "1.1.0", pubspec: {
-        "environment": {"sdk": ">=0.1.2 <0.2.0"}
+        "environment": {
+          "sdk": ">=0.1.2 <0.2.0"
+        }
       });
       builder.serve("foo", "1.2.0", pubspec: {
-        "environment": {"sdk": ">=0.1.3 <0.2.0"}
+        "environment": {
+          "sdk": ">=0.1.3 <0.2.0"
+        }
       });
     });
 
     schedulePub(args: ["global", "activate", "foo"]);
 
     // foo 1.2.0 won't be picked because its SDK constraint conflicts with the
     // dummy SDK version 0.1.2+3.
-    d.dir(cachePath, [
-      d.dir('global_packages', [
-        d.dir('foo', [d.matcherFile('pubspec.lock', contains('1.1.0'))])
-      ])
-    ]).validate();
+    d.dir(
+        cachePath,
+        [
+            d.dir(
+                'global_packages',
+                [
+                    d.dir('foo', [d.matcherFile('pubspec.lock', contains('1.1.0'))])])]).validate();
   });
 }