Summary:
Move CheckBox JS files to FB internal
## Changelog:
[General] [Removed] This diff removes the CheckBox export from React Native. Internally, we are requiring CheckBox directly now and externally people will have to use the community maintained module.
Reviewed By: cpojer
Differential Revision: D20910775
fbshipit-source-id: 809e135dc3f68911ac0a004e6eafa8488f0d5327