CGroup API files: drop mem_cgroup_force_empty()

This function isn't needed - a NULL pointer in the cftype read function will
result in the same EINVAL response to userspace.
Signed-off-by: NPaul Menage <menage@google.com>
Cc: "Li Zefan" <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "YAMAMOTO Takashi" <yamamoto@valinux.co.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -880,17 +880,6 @@ static ssize_t mem_force_empty_write(struct cgroup *cont,
 	return ret;
 }
 
-/*
- * Note: This should be removed if cgroup supports write-only file.
- */
-static ssize_t mem_force_empty_read(struct cgroup *cont,
-				struct cftype *cft,
-				struct file *file, char __user *userbuf,
-				size_t nbytes, loff_t *ppos)
-{
-	return -EINVAL;
-}
-
 static const struct mem_cgroup_stat_desc {
 	const char *msg;
 	u64 unit;
@@ -947,7 +936,6 @@ static struct cftype mem_cgroup_files[] = {
 	{
 		.name = "force_empty",
 		.write = mem_force_empty_write,
-		.read = mem_force_empty_read,
 	},
 	{
 		.name = "stat",