[ReactNative] Fix some mount callback issues

Libraries/Utilities/mountSafeCallback.js

@@ -1,23 +0,0 @@
-/**
- * Copyright (c) 2015-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @providesModule mountSafeCallback
- * @flow
- */
-'use strict';
-
-var mountSafeCallback = function(context: ReactComponent, callback: ?Function): any {
-  return function() {
-    if (!callback || !context.isMounted()) {
-      return;
-    }
-    return callback.apply(context, arguments);
-  };
-};
-
-module.exports = mountSafeCallback;