Remove --harmony-async-await runtime flag

test/mjsunit/harmony/async-await-no-constructor.js

-// Copyright 2016 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --harmony-async-await --allow-natives-syntax
-
-'use strict';
-
-var resolved = Promise.resolve();
-var count = 0;
-
-Object.defineProperty(Promise.prototype, 'constructor',
-                      { get() { count++; return Promise; } })
-
-async function foo() {
-  await resolved;
-  return resolved;
-}
-
-async function bar() {
-  throw 1;
-}
-
-foo();
-bar();
-%RunMicrotasks();
-assertEquals(1, count);