filemap: remove readahead_page()

Patch series "Misc folio patches for 6.16".

Remove a few APIs that we've converted everybody from using.  I also found
a few places that extract a page pointer from i_pages, which will be an
invalid thing to do when we separate pages from folios.


This patch (of 8):

All filesystems have now been converted to call readahead_folio() so we
can delete this wrapper.

Link: https://lkml.kernel.org/r/20250402210612.2444135-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20250402210612.2444135-2-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>