Update license headers for MIT license

Summary:
Includes React Native and its dependencies Fresco, Metro, and Yoga. Excludes samples/examples/docs.

find: ^(?:( *)|( *(?:[\*~#]|::))( )? *)?Copyright (?:\(c\) )?(\d{4})\b.+Facebook[\s\S]+?BSD[\s\S]+?(?:this source tree|the same directory)\.$
replace: $1$2$3Copyright (c) $4-present, Facebook, Inc.\n$2\n$1$2$3This source code is licensed under the MIT license found in the\n$1$2$3LICENSE file in the root directory of this source tree.

Reviewed By: TheSavior, yungsters

Differential Revision: D7007050

fbshipit-source-id: 37dd6bf0ffec0923bfc99c260bb330683f35553e

SliderExample.js

@@ -1,10 +1,8 @@
 /**
  * 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.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
  *
  * @flow
  * @providesModule SliderExample