mm: memcontrol: remove stale page_cgroup_lock comment

There is no cgroup-specific page lock anymore.

Signed-off-by: Johannes Weiner <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/memcontrol.c

···
 	int isolated;
 
 	VM_BUG_ON_PAGE(pc->mem_cgroup, page);
-	/*
-	 * we don't need page_cgroup_lock about tail pages, becase they are not
-	 * accessed by any other context at this point.
-	 */
 
 	/*
 	 * In some cases, SwapCache and FUSE(splice_buf->radixtree), the page