Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/global/binstubs/unknown_explicit_executable_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_stream.dart';
-
-import '../../../lib/src/exit_codes.dart' as exit_codes;
-import '../../descriptor.dart' as d;
-import '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration("errors on an unknown explicit executable", () {
-    d.dir("foo", [d.pubspec({
-        "name": "foo",
-        "executables": {
-          "one": "one"
-        }
-      }),
-          d.dir("bin", [d.file("one.dart", "main() => print('ok');")])]).create();
-
-    var pub = startPub(
-        args: [
-            "global",
-            "activate",
-            "--source",
-            "path",
-            "../foo",
-            "-x",
-            "who",
-            "-x",
-            "one",
-            "--executable",
-            "wat"]);
-
-    pub.stdout.expect(consumeThrough("Installed executable one."));
-    pub.stderr.expect("Unknown executables wat and who.");
-    pub.shouldExit(exit_codes.DATA);
-  });
-}