mm: remove unused page_is_file_lru() function

mm: remove unused page_is_file_lru() function

The page_is_file_lru() wrapper function is no longer used.  The kernel has
moved to folio-based APIs, and all callers should use folio_is_file_lru()
instead.

Remove the obsolete page-based wrapper function.

Link: https://lkml.kernel.org/r/20260323090305.798057-1-ye.liu@linux.dev
Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>