Fix: We cannot offer a Ref::delete(self), but a Ref::delete_by_hash()
Fix: We cannot offer a Ref::delete(self), but a Ref::delete_by_hash()

We cannot offer the former because deleting self would always fail as
the FileLockEntry is already borrowed from the store, so the store
declines this.

But deleting by hash works.

matthiasbeyer/imag,mario-kr/imag,matthiasbeyer/imag,mario-kr/imag