Remove g_object_unref() calls at the end of main

They trigger SIGBUS upon exit on OpenBSD (a sign of double-free?) and valgrind
complains loudly about them on Linux.

src/main.c

@@ -255,10 +255,6 @@ int main (int argc, char *argv[])
 
 	if (timeout > 0)
 		g_source_remove (timeout);
-	g_object_unref (window);
-	g_object_unref (status_icon);
-	g_object_unref (task_manager);
-	g_object_unref (settings);
 
 	return 0;
 }