mm/page_alloc.c: remove duplicate inclusion of page_ext.h

Link: http://lkml.kernel.org/r/20170202011942.1609-1-standby24x7@gmail.comSigned-off-by: NMasanari Iida <standby24x7@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -59,7 +59,6 @@
 #include <linux/prefetch.h>
 #include <linux/mm_inline.h>
 #include <linux/migrate.h>
-#include <linux/page_ext.h>
 #include <linux/hugetlb.h>
 #include <linux/sched/rt.h>
 #include <linux/page_owner.h>