Unbreak wheel event handling in QChartView

Reverts in practice e757445355, which
removed wheel event handling in QChartView completely, and - by not
even explicitly ignoring the event - broke event propagation to a parent
that might want to handle the wheel event (such as a parent scrollview).

Testing the reproducer from QTBUG-77403 shows that the problem stays
fixed anyway, probably through the general fixes to wheel-event handling
and propagation in 92df790f46b3a8b17aec2f385d6472fd3f8647f6.

Fixes: QTBUG-119712
Task-number: QTBUG-77403
Pick-to: 6.6 6.5
Change-Id: Icb94172659e0c4f41d7538d1e2432b6e4c548afe
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>

src/charts/qchartview.cpp

@@ -250,9 +250,7 @@ void QChartView::mouseReleaseEvent(QMouseEvent *event)
 #if QT_CONFIG(wheelevent)
 void QChartView::wheelEvent(QWheelEvent *event)
 {
-    Q_UNUSED(event);
-    // We just need to override wheelEvent, or scrolling won't work correctly on macOS trackpad
-    // (QTBUG-77403)
+    QGraphicsView::wheelEvent(event);
 }
 #endif
 #endif