nfs4: remove duplicated #include

Remove duplicated #include('s) in
  fs/nfs/nfs4proc.c

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -51,7 +51,6 @@
 #include <linux/sunrpc/bc_xprt.h>
 #include <linux/xattr.h>
 #include <linux/utsname.h>
-#include <linux/mm.h>
 
 #include "nfs4_fs.h"
 #include "delegation.h"