Code review comment for lp://qastaging/~alan-griffiths/mir/fix-1535894-alt

> 3. This looks like important code that will cause regressions if removed:
> - int result = scene_changed ? 1 : 0;
>
> That tells us to redraw the screen if a window has been dragged, but no
> windows contents changed. Obviously was missing a test.

Obviously, this code duplicated the effect of CompositingFunctor::schedule_compositing(int num) and was redundant.