[fix] remove 'use strict' from warnValidStyle

docs/storybook/3-demos/Game2048/Game2048.js

@@ -14,7 +14,6 @@
  * @providesModule Game2048
  * @flow
  */
-'use strict';
 
 import { any, func, object } from 'prop-types';
 import GameBoard from './GameBoard';

docs/storybook/3-demos/Game2048/GameBoard.js

@@ -14,7 +14,6 @@
  * @providesModule GameBoard
  * @flow
  */
-'use strict';
 
 // NB: Taken straight from: https://github.com/IvanVergiliev/2048-react/blob/master/src/board.js
 //     with no modification except to format it for CommonJS and fix lint/flow errors

src/vendor/warnValidStyle/index.js

@@ -11,8 +11,6 @@
  * @providesModule warnValidStyle
  */
 
-'use strict';
-
 var emptyFunction = require('fbjs/lib/emptyFunction');
 
 var warnValidStyle = emptyFunction;