Revert the chunk from r330410 in vm_page_reclaim_run().

There, the pages freed might be managed but the page's lock is not
owned. For KPI correctness, the page lock is requried around the call
to vm_page_free_prep(), which is asserted. Reclaim loop already did
the work which could be done by vm_page_free_prep(), so the lock is
not needed and the only consequence of not owning it is the assert
trigger.

Instead of adding the locking to satisfy the assert, revert to the
code that calls vm_page_free_phys() directly.

Reported by: pho
Discussed with: jeff
Sponsored by: The FreeBSD Foundation
MFC after: 1 week