mm, vmscan: remove redundant check in shrink_zones()

As pointed out by Minchan Kim, shrink_zones() checks for populated zones
in a zonelist but a zonelist can never contain unpopulated zones.  While
it's not related to the node-lru series, it can be cleaned up now.

Link: http://lkml.kernel.org/r/1468853426-12858-2-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Suggested-by: Minchan Kim <minchan@kernel.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b3f5b35..4978ee9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2605,9 +2605,6 @@
 
 	for_each_zone_zonelist_nodemask(zone, z, zonelist,
 					sc->reclaim_idx, sc->nodemask) {
-		if (!populated_zone(zone))
-			continue;
-
 		/*
 		 * Take care memory controller reclaiming has small influence
 		 * to global LRU.