Remove async_await dependency

DEPS

 # Copyright (c) 2012, 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.
 
 vars = {
   # The dart_root is the root of our sdk checkout. This is normally
   # simply sdk, but if using special gclient specs it can be different.
   "dart_root": "sdk",
 
   # The svn location to pull out dependencies from
@@ skipping 30 matching lines @@
   "analyzer_cli_rev" : "@090c4859a2f88e62ae71a11583ba31e9999c74f6",
   "args_tag": "@0.13.0",
   "barback_rev" : "@29ee90dbcf77cfd64632fa2797a4c8a4f29a4b51",
   "charcode_tag": "@1.1.0",
   "chrome_rev" : "@19997",
   "clang_rev" : "@28450",
   "cli_util_tag" : "@0.0.1+2",
   "collection_rev": "@1da9a07f32efa2ba0c391b289e2037391e31da0e",
   "crypto_rev" : "@2df57a1e26dd88e8d0614207d4b062c73209917d",
   "csslib_tag" : "@0.12.0",
-  "async_await_rev" : "@8b401a9f2e5e81dca5f70dbe7564112a0823dee6",
   "dartdoc_tag" : "@v0.0.2+2",
   "dart_services_rev" : "@7aea2574e6f3924bf409a80afb8ad52aa2be4f97",
   "dart_style_tag": "@0.1.8",
   "fake_async_rev" : "@38614",
   "firefox_jsshell_rev" : "@45554",
   "glob_rev": "@704cf75e4f26b417505c5c611bdaacd8808467dd",
   "gsutil_rev" : "@33376",
   "html_tag" : "@0.12.1+1",
   "http_rev" : "@9b93e1542c753090c50b46ef1592d44bc858bfe7",
   "http_multi_server_tag" : "@1.3.2",
@@ skipping 110 matching lines @@
       Var("observatory_pub_packages_rev"),
 
   Var("dart_root") + "/third_party/dart-services":
       (Var("github_mirror") % "dart-services") +
       Var("dart_services_rev"),
 
   Var("dart_root") + "/third_party/pkg/analyzer_cli":
       (Var("github_mirror") % "analyzer_cli") + Var("analyzer_cli_rev"),
   Var("dart_root") + "/third_party/pkg/args":
       (Var("github_mirror") % "args") + Var("args_tag"),
-  Var("dart_root") + "/third_party/pkg/async_await":
-      (Var("github_mirror") % "async_await") + Var("async_await_rev"),
   Var("dart_root") + "/third_party/pkg/barback":
       (Var("github_mirror") % "barback") + Var("barback_rev"),
   Var("dart_root") + "/third_party/pkg/charcode":
       (Var("github_mirror") % "charcode") + Var("charcode_tag"),
   Var("dart_root") + "/third_party/pkg/cli_util":
       (Var("github_mirror") % "cli_util") + Var("cli_util_tag"),
   Var("dart_root") + "/third_party/pkg/collection":
       (Var("github_mirror") % "collection") + Var("collection_rev"),
   Var("dart_root") + "/third_party/pkg/crypto":
       (Var("github_mirror") % "crypto") + Var("crypto_rev"),
@@ skipping 157 matching lines @@
       '--no_resume',
       '--bucket',
       'dart-dependencies',
       '-d',
       '-r',
       Var('dart_root') + '/third_party/d8',
     ],
   },
 
 ]