ns_cgroup: remove unused spinlock

I happened to find the spinlock in struct ns_cgroup is never used.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/ns_cgroup.c

@@ -13,7 +13,6 @@
 
 struct ns_cgroup {
 	struct cgroup_subsys_state css;
-	spinlock_t lock;
 };
 
 struct cgroup_subsys ns_subsys;
@@ -84,7 +83,6 @@ static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss,
 	ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);
 	if (!ns_cgroup)
 		return ERR_PTR(-ENOMEM);
-	spin_lock_init(&ns_cgroup->lock);
 	return &ns_cgroup->css;
 }