mm: remove page_mapping_file()

This function has no more users.

Link: https://lkml.kernel.org/r/20230802151406.3735276-31-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/pagemap.h

@@ -414,14 +414,6 @@ static inline struct address_space *page_file_mapping(struct page *page)
 	return folio_file_mapping(page_folio(page));
 }
 
-/*
- * For file cache pages, return the address_space, otherwise return NULL
- */
-static inline struct address_space *page_mapping_file(struct page *page)
-{
-	return folio_flush_mapping(page_folio(page));
-}
-
 /**
  * folio_inode - Get the host inode for this folio.
  * @folio: The folio.