Remove --harmony-async-await runtime flag

test/mjsunit/es8/async-arrow-lexical-new.target.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
+// Flags: --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() +
@@ skipping 18 matching lines @@
 class BaseClass {
   constructor() {
     return async () => new.target;
   }
 }
 
 class ChildClass extends BaseClass {}
 
 assertEqualsAsync(BaseClass, () => new BaseClass()());
 assertEqualsAsync(ChildClass, () => new ChildClass()());