Remove ReactTypes from fbsource and React sync

Summary:
See facebook/react#18366

This contains a fork of the upstream Flow types. We shouldn't be syncing this since these leads to conflicting types.

As a result, these uses have already been codemodded away. Only the imports remained.

Changelog:

[React Core] - Remove ReactTypes from sync.

Reviewed By: gaearon

Differential Revision: D20583740

fbshipit-source-id: fc86a934cbdca8ff90fe90282b86ecc945a85e5f

Author: sebmarkbage