virtio-vdpa: Remove virtqueue list

The virtio vdpa implementation creates a list of virtqueues, while the
same is already available in the struct virtio_device.

This list is never traversed though, and only the pointer to the struct
virtio_vdpa_vq_info is used in the callback, where the virtqueue pointer
could be directly used.

Remove the unwanted code to simplify the driver.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Message-Id: <7808f2f7e484987b95f172fffb6c71a5da20ed1e.1748503784.git.viresh.kumar@linaro.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>