Remove manual wire_count adjustments.

[markj]

Summary

Also use vm_page_free() instead of vm_page_free_toq(). This should have
no effect, since the pages freed here were allocated without
VM_ALLOC_ZERO and thus do not have PG_ZERO set. However, if that were
to change, we would potentially be telling the VM that the page is
zero-filled when nothing ensures that that's the case.