mm/ksm: remove unused page_referenced_ksm declaration

Commit 9f32624be9 ("mm/rmap: use rmap_walk() in page_referenced()")
removed the declaration of page_referenced_ksm for the case
CONFIG_KSM=y, but left one for CONFIG_KSM=n.

Remove the unused leftover.

Link: http://lkml.kernel.org/r/1524552106-7356-2-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/ksm.h

@@ -89,12 +89,6 @@ static inline struct page *ksm_might_need_to_copy(struct page *page,
 	return page;
 }
 
-static inline int page_referenced_ksm(struct page *page,
-			struct mem_cgroup *memcg, unsigned long *vm_flags)
-{
-	return 0;
-}
-
 static inline void rmap_walk_ksm(struct page *page,
 			struct rmap_walk_control *rwc)
 {