virtio-mmio: Revert "virtio_mmio: support the arg sizes of find_vqs()"

This reverts commit fbed86ab.
The API is now unused, let's not carry dead code around.

Fixes: fbed86ab ("virtio_mmio: support the arg sizes of find_vqs()")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20220816053602.173815-4-mst@redhat.com>