Remove a completely bogus reference increment in the Xen driver.

xenUnifiedDomainEventRegister() calls out to
virDomainEventCallbackListAdd(), which increments the reference
count on the connection.  That is fine, but then
xenUnifiedDomainEventRegister() increments the usage count again,
leading to a usage count leak.  Remove the increment in the xen
register, and the UnrefConnect in the xen unregister.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

src/xen/xen_driver.c

@@ -1502,9 +1502,6 @@ xenUnifiedDomainEventRegister (virConnectPtr conn,
     ret = virDomainEventCallbackListAdd(conn, priv->domainEventCallbacks,
                                         callback, opaque, freefunc);
 
-    if (ret == 0)
-        conn->refs++;
-
     xenUnifiedUnlock(priv);
     return (ret);
 }
@@ -1530,9 +1527,6 @@ xenUnifiedDomainEventDeregister (virConnectPtr conn,
         ret = virDomainEventCallbackListRemove(conn, priv->domainEventCallbacks,
                                                callback);
 
-    if (ret == 0)
-        virUnrefConnect(conn);
-
     xenUnifiedUnlock(priv);
     return ret;
 }