virto_net: remove empty file 'virtio_net.'

Looks like this was mistakenly added to the tree as part of
commit 186b3c998c50 ("virtio-net: support XDP_REDIRECT").

Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>