Any file with access to object_event_private.h also has access to
the internals of virObjectEvent, without needing an accessor
function.  Not to mention the accessor function was doing type
checks that would always succeed.

* src/conf/object_event_private.h (virObjectEventGetEventID): Drop.
* src/conf/object_event.c (virObjectEventGetEventID): Drop.
(virObjectEventDispatchMatchCallback): Simplify caller.
* src/conf/domain_event.c (virDomainEventDispatchDefaultFunc):
Likewise.
Signed-off-by: NEric Blake <eblake@redhat.com>