kill unused invalidate_inode_pages helper

No one is calling this anymore as everyone has switched to
invalidate_mapping_pages long time ago.  Also update a few
references to it in comments.  nfs has two more, but I can't
easily figure what they are actually referring to, so I left
them as-is.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/mm/filemap.c b/mm/filemap.c
index 698ea80..148b52a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1117,7 +1117,7 @@
 			if (!PageUptodate(page)) {
 				if (page->mapping == NULL) {
 					/*
-					 * invalidate_inode_pages got it
+					 * invalidate_mapping_pages got it
 					 */
 					unlock_page(page);
 					page_cache_release(page);