vmscan: zone_reclaim don't call disable_swap_token()

Swap token don't works when zone reclaim is enabled since it was born.
Because __zone_reclaim() always call disable_swap_token() unconditionally.

This kill swap token feature completely.  As far as I know, nobody want to
that.  Remove it.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -2592,7 +2592,6 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 	};
 	unsigned long slab_reclaimable;
 
-	disable_swap_token();
 	cond_resched();
 	/*
 	 * We need to be able to allocate from the reserves for RECLAIM_SWAP