NFSD: Remove lockdep assertion from unhash_and_release_locked()

[ Upstream commit f53cef15 ]

IIUC, holding the hash bucket lock is needed only in
nfsd_file_unhash, and there is already a lockdep assertion there.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>