[GUI] Remove code for Qt < 5.9

src/Gui/WaitCursor.cpp

@@ -33,9 +33,7 @@
 # endif
 #endif
 
-#if QT_VERSION >= 0x050000
-# include <QWindow>
-#endif
+#include <QWindow>
 
 #include "WaitCursor.h"
 
@@ -105,13 +103,11 @@ void WaitCursorP::setIgnoreEvents(WaitCursor::FilterEventsFlags flags)
 bool WaitCursorP::isModalDialog(QObject* o) const
 {
     QWidget* parent = qobject_cast<QWidget*>(o);
-#if QT_VERSION >= 0x050000
     if (!parent) {
         QWindow* window = qobject_cast<QWindow*>(o);
         if (window)
             parent = QWidget::find(window->winId());
     }
-#endif
     while (parent) {
         QMessageBox* dlg = qobject_cast<QMessageBox*>(parent);
         if (dlg && dlg->isModal())