virtio_vdpa: Revert "virtio_vdpa: support the arg sizes of find_vqs()"

This reverts commit 99e8927d:
proposed API isn't supported on all transports but no
effort was made to address this.

It might not be hard to fix if we want to: maybe just rename size to
size_hint and make sure legacy transports ignore the hint.

But it's not sure what the benefit is in any case, so let's drop it.

Fixes: 99e8927d ("virtio_vdpa: support the arg sizes of find_vqs()")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20220816053602.173815-6-mst@redhat.com>