Remove loadVectorDrawablesOnImages feature flag (#49183)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49183

The feature has been released to all for quite some time now and the holdout group has finally been unlinked. This removes all references to the feature flag and a few indicators that the feature is enabled/disabled from RNTester

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D69146787

fbshipit-source-id: 8a7f01016a715e61541910630d8c3ceb84ec5c82