mm/vmstat: remove unused page_ext.h from vmstat

No page_ext function or structure is used in vmstat.  Just remove page_ext
header from vmstat.

Link: https://lkml.kernel.org/r/20230717113227.1897173-3-shikemeng@huaweicloud.comSigned-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmstat.c

@@ -26,7 +26,6 @@
 #include <linux/writeback.h>
 #include <linux/compaction.h>
 #include <linux/mm_inline.h>
-#include <linux/page_ext.h>
 #include <linux/page_owner.h>
 #include <linux/sched/isolation.h>