Gui: [skip ci] Revert workaround to avoid to handle wheel events twice inside the 3d view

This workaround caused a regression with Qt 5.15. For more details see: https://forum.freecadweb.org/viewtopic.php?f=3&t=50231

src/Gui/Quarter/QuarterWidget.cpp

@@ -1003,20 +1003,7 @@ bool QuarterWidget::viewportEvent(QEvent* event)
         QMouseEvent* mouse = static_cast<QMouseEvent*>(event);
         QGraphicsItem *item = itemAt(mouse->pos());
         if (!item) {
-            bool ok = QGraphicsView::viewportEvent(event);
-            // Avoid that wheel events are handled twice
-            // https://forum.freecadweb.org/viewtopic.php?f=3&t=44822
-            // However, this workaround seems to cause a regression on macOS
-            // so it's disabled for this platform.
-            // https://forum.freecadweb.org/viewtopic.php?f=4&t=44855
-#if defined(Q_OS_MAC)
-            Q_UNUSED(ok)
-#else
-            if (event->type() == QEvent::Wheel) {
-                event->setAccepted(ok);
-                return ok;
-            }
-#endif
+            QGraphicsView::viewportEvent(event);
             return false;
         }
     }