Remove REGISTRY_FF_ENFORCE_LOCKFILES

Context

Preventing a filesystem metadata registry from ... (#1335 - closed) introduced the feature flag REGISTRY_FF_ENFORCE_LOCKFILES which prevents the registry from starting if any of the lock files exists database-in-use and filesystem-in-use and the wrong configuration is used.

Implementation

Once we are done rolling out the FF Rollout REGISTRY_FF_ENFORCE_LOCKFILES on gitlab... (#1438 - closed), we should remove it from the code base.