Summary:
These comments were confusing since we don't use flow-typed.
cc bvaughn.
I have replaced our local types by flow-typed, removed metro custom stub and deleted `flow-github` directory.
As result, createReactClass, PropTypes and Metro types won't be distributed to RN users. If you need it, you should relay on flow-typed.
Pull Request resolved: https://github.com/facebook/react-native/pull/20320
Reviewed By: TheSavior
Differential Revision: D13517157
Pulled By: rickhanlonii
fbshipit-source-id: e52c0b6114114a706f6152b2031c600e3dece0d2