mm/migrate.c: remove the unused macro lru_to_page

lru_to_page is not used in mm/migrate.c.
Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -39,8 +39,6 @@
 
 #include "internal.h"
 
-#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
-
 /*
  * migrate_prep() needs to be called before we start compiling a list of pages
  * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is