[libkwineffects] Don't mark a painted window as transformed twice

Summary:
WindowPrePaintData::setTransformed sets PAINT_WINDOW_TRANSFORMED,
so `data.mask |= PAINT_WINDOW_TRANSFORMED;` is redundant.

Test Plan: Minimized a window, haven't noticed visual glitches.

Reviewers: #kwin, davidedmundson, graesslin

Reviewed By: #kwin, davidedmundson, graesslin

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D17565

libkwineffects/kwinanimationeffect.cpp

@@ -591,7 +591,6 @@ void AnimationEffect::prePaintWindow( EffectWindow* w, WindowPrePaintData& data,
                     data.setTranslucent();
                 else if (!(anim->attribute == Brightness || anim->attribute == Saturation)) {
                     data.setTransformed();
-                    data.mask |= PAINT_WINDOW_TRANSFORMED;
                     if (anim->attribute == Clip)
                         clipWindow(w, *anim, data.quads);
                 }