memcg: fix stale mem_cgroup_force_empty() comment

Commit f61c42a7d911 ("memcg: remove tasks/children test from
mem_cgroup_force_empty()") removed memory reparenting from the function.

Fix the function's comment.

Link: http://lkml.kernel.org/r/1462569810-54496-1-git-send-email-gthelen@google.com
Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2652,8 +2652,7 @@ static inline bool memcg_has_children(struct mem_cgroup *memcg)
 }
 
 /*
- * Reclaims as many pages from the given memcg as possible and moves
- * the rest to the parent.
+ * Reclaims as many pages from the given memcg as possible.
  *
  * Caller is responsible for holding css reference for memcg.
  */