Remove --harmony-async-await runtime flag

test/mjsunit/es8/async-await-basic.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
 
 // Do not install `AsyncFunction` constructor on global object
 
 function assertThrowsAsync(run, errorType, message) {
   var actual;
   var hadValue = false;
   var hadError = false;
   var promise = run();
 
   if (typeof promise !== "object" || typeof promise.then !== "function") {
@@ skipping 367 matching lines @@
     "20", () => (async(foo, { a = "0" }) => foo + a)("2", { a: undefined }));
 assertThrows(() => eval("async({ foo = 1 })"), SyntaxError);
 assertThrows(() => eval("async(a, { foo = 1 })"), SyntaxError);
 
 // https://bugs.chromium.org/p/chromium/issues/detail?id=638019
 async function gaga() {
   let i = 1;
   while (i-- > 0) { await 42 }
 }
 assertDoesNotThrow(gaga);