Summary:
This removes the use of the legacy context API in `TextInput`.
Nothing in OSS appears to make use of the `focusEmitter`.
Pull Request resolved: https://github.com/facebook/react-native/pull/22220
Reviewed By: TheSavior
Differential Revision: D13408886
Pulled By: RSNara
fbshipit-source-id: 9ae597507ccc26a9bc944a44c1f51b91e73cd637