Remove runtime flags for Proxy and Reflect

test/mjsunit/es6/proxies-is-extensible.js

 // Copyright 2015 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-proxies --harmony-reflect
-
 
 (function () {
   // No trap.
 
   var target = {};
   var handler = {};
   var proxy = new Proxy(target, handler);
 
   assertTrue(Reflect.isExtensible(target));
   assertTrue(Reflect.isExtensible(proxy));
@@ skipping 48 matching lines @@
   var handler = { isExtensible() {return 0} };
   var proxy = new Proxy(target, handler);
 
   // Trap returns falsish but target is extensible.
   assertThrows(() => {Reflect.isExtensible(proxy)}, TypeError);
 
   // Trap returns falsish and target is not extensible.
   Reflect.preventExtensions(target);
   assertFalse(Reflect.isExtensible(proxy));
 })();