We might as well take advantage of viralloc.h instead of open-coding
array management ourselves.  While at it, I simplified several
places that were doing repetitive pointer chasing to use an
intermediate variable for legibility (some other places remain,
but they will disapper in later refactoring patches).

* src/conf/object_event_private.h (_virObjectEventCallbackList):
Use size_t for count.
* src/conf/object_event.c (_virObjectEventQueue): Likewise.
(virObjectEventCallbackListRemoveID): Use VIR_DELETE_ELEMENT.
(virObjectEventQueuePush, virObjectEventCallbackListAddID): Use
VIR_APPEND_ELEMENT.
(virObjectEventCallbackListEventID)
(virObjectEventStateDispatchCallbacks): Simplify code.
Signed-off-by: NEric Blake <eblake@redhat.com>