See r338276. It is not sufficient to return immediately if
m->queue == PQ_NONE since another thread may be update the page's
queue state concurrently. vm_page_dequeue() now just returns if the
page is not enqueued (prior to r332974 it would panic in this case), so
simply replace all vm_page_remque() calls with vm_page_dequeue()
calls.

The problem was found while reading code. Peter is testing
this patch.