Some code simplifications

1. `number_width` isn't used later
2. `return_type` is used only once
3. AudioServer::get_singleton()->get_channel_count() always returns a channel_count of 1 or larger
4. negative `aa->backward` conditional
5. `current_canvas` == `find_world_2d()->get_canvas()`
6. identical if `render_shadows`

scene/animation/animation_player.cpp

@@ -1233,7 +1233,7 @@ void AnimationPlayer::_animation_update_transforms() {
 					if (aa->time < pasi.start) {
 						stop = true;
 					}
-				} else if (aa->backward) {
+				} else {
 					if (aa->time > pasi.start) {
 						stop = true;
 					}