qt: don't scale radius for drop shadow effect

radius is not scaled in QPixmapDropShadowFilter[1], so I don't see why we should scale it here

improves scene graph batching and reduces size of generated effect

shadow node size and batching comparison -

master	this MR

[1] https://codebrowser.dev/qt5/qtbase/src/widgets/effects/qpixmapfilter.cpp.html#1340

(cc @fuzun)