rpc: remove unused typedef for auto shutdown function callback

The use of the virNetServerAutoShutdownFunc typedef was removed in

commit 79b8a56995e6d9ce47e0b44512f7be440df9ff7d
Author: Daniel P. Berrange <berrange@redhat.com>
Date: Wed Oct 31 19:03:55 2012 +0000

Replace polling for active VMs with signalling by drivers

This unused typedef was then copied into the virNetDaemon object
when that was split off from virNetServer, resulting in a typedef
virNetDaemonAutoShutdownFunc that has never been needed.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>