Replace our local types by flow-typed (react#20320)

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: react#20320

Reviewed By: TheSavior

Differential Revision: D13517157

Pulled By: rickhanlonii

fbshipit-source-id: e52c0b6114114a706f6152b2031c600e3dece0d2

Author: charpeni

.flowconfig

@@ -31,7 +31,6 @@
 [libs]
 Libraries/react-native/react-native-interface.js
 flow/
-flow-github/
 
 [options]
 emoji=true

.flowconfig.android

@@ -31,7 +31,6 @@
 [libs]
 Libraries/react-native/react-native-interface.js
 flow/
-flow-github/
 
 [options]
 emoji=true

flow-github/metro.js

@@ -9,7 +9,8 @@
  * @nolint
  */
 
-// TODO (acdlite) Remove this file once flowtype/flow-typed/pull/773 is merged
+// flow-typed signature: 892fd8dcd3f17e76da4fb1334b0fd49e
+// flow-typed version: da30fe6876/create-react-class_v15.x.x/flow_>=v0.41.x
 
 declare module 'create-react-class' {
   declare module.exports: React$CreateClass;