fix: Remove BackHandler.removeEventListener

[retyui]

Summary:

All removeEventListener methods was removed 2596b2f perviously but seems a BackHandler was missed

This can be a breaking change for some third-party modules.

Migration: Use remove on the EventSubscription from addEventListener:

useEffect(() => {
+  const subscription = NativeModule.removeListener(name, listener);
+  return () => subscription.remove();
}, []);

Changelog:

[GENERAL] [REMOVED] - Remove BackHandler.removeEventListener

Test Plan:

...

[facebook-github-bot]

@javache has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@javache merged this pull request in 44d6194.

[react-native-bot]

This pull request was successfully merged by @retyui in 44d6194

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