Remove dead Inspector.kt/JInspector.h/.cpp code (#53403)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/53403

This code is Legacy and totally unused. It should be safe to remove it altogether.
This class is public but no one is using it in OSS + no one should be using it, so I don't think we'll need the full deprecation cycle for it.

Changelog:
[Android] [Removed] - Removed unused `Inspector` public class from React Android

Reviewed By: cipolleschi

Differential Revision: D80711515

fbshipit-source-id: 83134851877fcbccd50f7a5b75b2ab8906b3416a