Clean up unused mock for NavigationRootContainer

Reviewed By: fkgozali

Differential Revision: D3859089

fbshipit-source-id: 265488e88c09aed59c465aa9c3b93e84937659d4

Libraries/NavigationExperimental/__mocks__/NavigationRootContainer.js

@@ -1,16 +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.
- */
-
-const NavigationRootContainer = {
-  getBackAction: () => {
-    return { type: 'BackAction' };
-  }
-};
-
-module.exports = NavigationRootContainer;