NFSv4: remove nfs4_renewd_prepare_shutdown() declaration

nfs4_renewd_prepare_shutdown() has been removed since
commit 3050141b ("NFSv4: Kill nfs4_renewd_prepare_shutdown()"),
so remove it.
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/nfs4_fs.h

@@ -459,7 +459,6 @@ struct nfs_client *nfs4_alloc_client(const struct nfs_client_initdata *);
 
 /* nfs4renewd.c */
 extern void nfs4_schedule_state_renewal(struct nfs_client *);
-extern void nfs4_renewd_prepare_shutdown(struct nfs_server *);
 extern void nfs4_kill_renewd(struct nfs_client *);
 extern void nfs4_renew_state(struct work_struct *);
 extern void nfs4_set_lease_period(struct nfs_client *clp, unsigned long lease);