remove misleading/incorrect comment

The previously-commented code is precisely what gets invoked
when solo state changes, and had nothing to do with actually
changing solo state in any way.

libs/surfaces/mackie/strip.cc

@@ -287,8 +287,6 @@ void
 Strip::notify_solo_changed ()
 {
 	if (_stripable && _solo) {
-		// TODO use session->set_control(), subscribe to solo_control changes later
-		// call_surface->write(), see 9d8829f5bf
 		_surface->write (_solo->set_state (_stripable->solo_control()->soloed() ? on : off));
 	}
 }