swap: remove unused mem_cgroup_uncharge_swapcache declaration

The body of this function was removed by commit 0a31bc97c80c ("mm:
memcontrol: rewrite uncharge API").

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/shmem.c b/mm/shmem.c
index b3e4031..864c878 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1131,7 +1131,7 @@
 			 * truncated or holepunched since swap was confirmed.
 			 * shmem_undo_range() will have done some of the
 			 * unaccounting, now delete_from_swap_cache() will do
-			 * the rest (including mem_cgroup_uncharge_swapcache).
+			 * the rest.
 			 * Reset swap.val? No, leave it so "failed" goes back to
 			 * "repeat": reading a hole and writing should succeed.
 			 */