Remove --harmony-async-await runtime flag

test/mjsunit/harmony/async-arrow-lexical-this.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
-
-function assertEqualsAsync(expected, run, msg) {
-  var actual;
-  var hadValue = false;
-  var hadError = false;
-  var promise = run();
-
-  if (typeof promise !== "object" || typeof promise.then !== "function") {
-    throw new MjsUnitAssertionError(
-        "Expected " + run.toString() +
-        " to return a Promise, but it returned " + PrettyPrint(promise));
-  }
-
-  promise.then(function(value) { hadValue = true; actual = value; },
-               function(error) { hadError = true; actual = error; });
-
-  assertFalse(hadValue || hadError);
-
-  %RunMicrotasks();
-
-  if (hadError) throw actual;
-
-  assertTrue(
-      hadValue, "Expected '" + run.toString() + "' to produce a value");
-
-  assertEquals(expected, actual, msg);
-};
-
-var O = {
-  [Symbol.toStringTag]: "LexicalThis",
-  run(n) {
-    return async passFail => `${n}. ${passFail}: ${this}`;
-  },
-};
-
-assertEqualsAsync("1. PASS: [object LexicalThis]", () => O.run(1)("PASS"));
-
-var O2 = {
-  [Symbol.toStringTag]: "LexicalThis",
-  run: O.run(2)
-};
-
-assertEqualsAsync("2. PASS: [object LexicalThis]", () => O2.run("PASS"));