TextInput: Remove use of legacy context API (#22220)
TextInput: Remove use of legacy context API (#22220)

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

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