Remove --harmony-async-await runtime flag

test/mjsunit/es8/sloppy-no-duplicate-async.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
-
 // Async functions don't get sloppy-mode block-scoped function hoisting
 
 // No hoisting to the global scope
 
 {
   async function foo() {}
   assertEquals('function', typeof foo);
 }
 assertEquals('undefined', typeof foo);
 
 // No hoisting within a function scope
 (function() {
   { async function bar() {} }
   assertEquals('undefined', typeof bar);
 })();
 
 // Lexical shadowing allowed, no hoisting
 (function() {
   var y;
   async function x() { y = 1; }
   { async function x() { y = 2; } }
   x();
   assertEquals(1, y);
 })();