fs: Remove aops->launder_page

With all users converted to ->launder_folio, remove ->launder_page.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Acked-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Tested-by: Mike Marshall <hubcap@omnibond.com> # orangefs
Tested-by: David Howells <dhowells@redhat.com> # afs

Author: Matthew Wilcox (Oracle)

include/linux/fs.h

@@ -399,10 +399,7 @@ struct address_space_operations {
 			struct page *, struct page *, enum migrate_mode);
 	bool (*isolate_page)(struct page *, isolate_mode_t);
 	void (*putback_page)(struct page *);
-	union {
-		int (*launder_page) (struct page *);
-		int (*launder_folio) (struct folio *);
-	};
+	int (*launder_folio)(struct folio *);
 	bool (*is_partially_uptodate) (struct folio *, size_t from,
 			size_t count);
 	void (*is_dirty_writeback) (struct page *, bool *, bool *);