Remove runtime flags for Proxy and Reflect

test/mjsunit/harmony/proxies-object-assign.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
-
-var handler = {
-  ownKeys: function(t) { return ["a", "b"]; },
-  getOwnPropertyDescriptor: function(t, p) {
-    return {enumerable: true, configurable: true}
-  },
-  get: function(t, p) {
-    return 1;
-  }
-};
-
-var proxy = new Proxy({}, handler);
-
-var o = {};
-
-Object.assign(o, proxy);
-
-assertEquals({"a": 1, "b": 1}, o);
-
-(function TestStringSources() {
-  var source = "abc";
-  var target = {};
-  Object.assign(target, source);
-  assertEquals({0: "a", 1: "b", 2: "c"}, target);
-})();