NFSv4: Fix a compiler warning when CONFIG_NFS_V4_1 is undefined

Fix a compiler warning:
fs/nfs/nfs4proc.c:910:13: warning: 'nfs4_layoutget_release' defined but not used [-Wunused-function]
 static void nfs4_layoutget_release(void *calldata)
             ^~~~~~~~~~~~~~~~~~~~~~
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4proc.c

@@ -88,7 +88,6 @@
 	| ATTR_MTIME_SET)
 
 struct nfs4_opendata;
-static void nfs4_layoutget_release(void *calldata);
 static int _nfs4_recover_proc_open(struct nfs4_opendata *data);
 static int nfs4_do_fsinfo(struct nfs_server *, struct nfs_fh *, struct nfs_fsinfo *);
 static void nfs_fixup_referral_attributes(struct nfs_fattr *fattr);
@@ -907,10 +906,6 @@ nfs4_sequence_process_interrupted(struct nfs_client *client,
 
 #else	/* !CONFIG_NFS_V4_1 */
 
-static void nfs4_layoutget_release(void *calldata)
-{
-}
-
 static int nfs4_sequence_process(struct rpc_task *task, struct nfs4_sequence_res *res)
 {
 	return nfs40_sequence_done(task, res);