Fusion: Don't draw the background of the lineedit when drawing the frame

Since only the frame is being drawn here, it should only draw the
outline. Otherwise it will override any background drawing done via a
stylesheet.

Change-Id: I408fc44743747ad369c700b3d52935bfc8826f11
Fixes: QTBUG-71950
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/widgets/styles/qfusionstyle.cpp

@@ -725,7 +725,6 @@ void QFusionStyle::drawPrimitive(PrimitiveElement elem,
 
         // Draw Outline
         painter->setPen( QPen(hasFocus ? highlightedOutline : outline));
-        painter->setBrush(option->palette.base());
         painter->drawRoundedRect(r.adjusted(0, 0, -1, -1), 2, 2);
 
         if (hasFocus) {