mm: remove PageUnevictable

There is only one caller of PageUnevictable() left; convert it to call
folio_test_unevictable() and remove all the page accessors.

Link: https://lkml.kernel.org/r/20240821193445.2294269-6-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>