openvswitch: remove unused functions

ovs_vport_deferred_free is not used anywhere. It's the only caller of
free_vport_rcu thus this one can be removed, too.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>