Add test to assert Reflect.enumerate is now undefined

Ref #495

test/built-ins/Reflect/enumerate/undefined.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+id: sec-reflect-object
+description: >
+  Reflect.enumerate was removed and it's not a function anymore
+---*/
+
+assert.sameValue(Reflect.hasOwnProperty("enumerate"), false);
+assert.sameValue(Reflect.enumerate, undefined);