qquickfusionstyle: do not force a fixed blue color as highlight color

use the one from ... mac system palette.

Task-number: QTBUG-70652
Change-Id: I0aa9ab0596ceb8222327d9febbb132fffc3968cc
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

src/imports/controls/fusion/qquickfusionstyle.cpp

@@ -85,8 +85,6 @@ QColor QQuickFusionStyle::innerContrastLine()
 
 QColor QQuickFusionStyle::highlight(const QPalette &palette)
 {
-    if (isMacSystemPalette(palette))
-        return QColor(60, 140, 230);
     return palette.color(QPalette::Highlight);
 }