Clean up triggers awaiting global state modification at shutdown

Otherwise they can be reported as memory leaks since no more global
state modifications will take place to notify the trigger to clean
itself up.

src/main.cc

@@ -343,6 +343,7 @@ void terminate_bro()
 
 	mgr.Drain();
 
+	notifier::registry.Terminate();
 	log_mgr->Terminate();
 	input_mgr->Terminate();
 	thread_mgr->Terminate();