[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