Remove --harmony-modules flag and let embedder decide when modules are used

test/mjsunit/harmony/regress/regress-343928.js

-// Copyright 2014 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-modules --expose-debug-as=debug
-
-(function () {  // Scope for utility functions.
-  escaping_function = function(object) {
-    // Argument must not be null or undefined.
-    var string = Object.prototype.toString.call(object);
-    // String has format [object <ClassName>].
-    return string.substring(8, string.length - 1);
-  }
-})();
-
-module B {
-  var stuff = 3
-}
-
-var __v_0 = {};
-var __v_4 = debug.MakeMirror(__v_0);
-print(__v_4.referencedBy().length);  // core dump here if not fixed.