Remove unused feature flag related to TurboModule deadlock (#50479)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50479

In D72273163 the only reference to RN feature flag `throwExceptionInsteadOfDeadlockOnTurboModuleSetupDuringSyncRenderIOS` was removed, so this diff removes the feature flag. Also it removes remnants of D69922771 which are no longer needed.

Changelog: [Internal]

Reviewed By: shwanton

Differential Revision: D72427164

fbshipit-source-id: 398583ac14910a396839140c06011efa084fe04d