Move event-que declarations to sysdeps, new backend interface process_removed

- the reason being that the que-handling was declared on global level, but
  was only implemented in one back end.  If this is deemed generally useful,
  it should all be moved to front end, but as things are it's all the same,
  so I'm preferring the less invasive change
diff --git a/proc.c b/proc.c
index cd8f6cd..9a82782 100644
--- a/proc.c
+++ b/proc.c
@@ -570,23 +570,6 @@
 	return CBS_CONT;
 }
 
-static enum ecb_status
-event_for_proc(Event * event, void * data)
-{
-	if (event->proc == data)
-		return ecb_deque;
-	else
-		return ecb_cont;
-}
-
-static void
-delete_events_for(Process * proc)
-{
-	Event * event;
-	while ((event = each_qd_event(&event_for_proc, proc)) != NULL)
-		free(event);
-}
-
 void
 remove_process(Process *proc)
 {
@@ -596,7 +579,7 @@
 		each_task(proc, NULL, &clear_leader, NULL);
 
 	unlist_process(proc);
-	delete_events_for(proc);
+	process_removed(proc);
 	process_destroy(proc);
 	free(proc);
 }