mm: remove folio_test_transhuge()

This function is misleading; people think it means "Is this a THP", when
all it actually does is check whether this is a large folio.  Remove it;
the one remaining user should have been checking to see whether the folio
is PMD sized or not.

Link: https://lkml.kernel.org/r/20230816151201.3655946-12-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>