Revert "virtio_config: introduce a new .enable_cbs method"

This reverts commit d50497eb.

The new callback ended up not being used, and it's asymmetrical:
just enable, no disable.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

include/linux/virtio_config.h

@@ -23,8 +23,6 @@ struct virtio_shm_region {
  *       any of @get/@set, @get_status/@set_status, or @get_features/
  *       @finalize_features are NOT safe to be called from an atomic
  *       context.
- * @enable_cbs: enable the callbacks
- *      vdev: the virtio_device
  * @get: read the value of a configuration field
  *	vdev: the virtio_device
  *	offset: the offset of the configuration field
@@ -78,7 +76,6 @@ struct virtio_shm_region {
  */
 typedef void vq_callback_t(struct virtqueue *);
 struct virtio_config_ops {
-	void (*enable_cbs)(struct virtio_device *vdev);
 	void (*get)(struct virtio_device *vdev, unsigned offset,
 		    void *buf, unsigned len);
 	void (*set)(struct virtio_device *vdev, unsigned offset,
@@ -233,9 +230,6 @@ void virtio_device_ready(struct virtio_device *dev)
 {
 	unsigned status = dev->config->get_status(dev);
 
-	if (dev->config->enable_cbs)
-                  dev->config->enable_cbs(dev);
-
 	BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
 	dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
 }