mm/compaction: remove duplicated VM_BUG_ON_PAGE !PageLocked

The VM_BUG_ON_PAGE(!PageLocked(page), page) is also done in PageMovable.
Remove this explicitly one.

Link: https://lkml.kernel.org/r/20210109081420.46030-1-linmiaohe@huawei.com


Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>