vsock/virtio: remove unused 'work' field from 'struct virtio_vsock_pkt'

The 'work' field was introduced with commit 06a8fc7
("VSOCK: Introduce virtio_vsock_common.ko")
but it is never used in the code, so we can remove it to save
memory allocated in the per-packet 'struct virtio_vsock_pkt'

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/linux/virtio_vsock.h

@@ -48,7 +48,6 @@ struct virtio_vsock_sock {
 
 struct virtio_vsock_pkt {
 	struct virtio_vsock_hdr	hdr;
-	struct work_struct work;
 	struct list_head list;
 	/* socket refcnt not held, only use for cancellation */
 	struct vsock_sock *vsk;