[react-packager] Remove unnecessary 'chalk' module mock

packager/react-packager/src/Activity/__mocks__/chalk.js

@@ -1,13 +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.
- */
-'use strict';
-
-module.exports = {
-  dim: s =>  s,
-};