mm: simplify folio_migrate_mapping()

Now that folio_undo_large_rmappable() is an inline function checking
order and large_rmappable for itself (and __folio_undo_large_rmappable()
is now declared even when CONFIG_TRANASPARENT_HUGEPAGE is off) there is
no need for folio_migrate_mapping() to check large and large_rmappable
first (in the mapping case when it has had to freeze anyway).

Link: https://lkml.kernel.org/r/68feee73-050e-8e98-7a3a-abf78738d92c@google.com


Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>