nfs: Remove unused list nfs4_clientid_list

This list was designed to store struct nfs4_client in the client side.
But nfs4_client was obsolete and has been removed from the source code.
So remove the unused list.
Signed-off-by: Yanchuan Nian <ycnian@gmail.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4state.c

@@ -67,7 +67,6 @@
 
 const nfs4_stateid zero_stateid;
 static DEFINE_MUTEX(nfs_clid_init_mutex);
-static LIST_HEAD(nfs4_clientid_list);
 
 int nfs4_init_clientid(struct nfs_client *clp, struct rpc_cred *cred)
 {