Drop code variant for no longer supported Qt versions

GIT_SILENT

src/mainwindow.cpp

@@ -129,11 +129,7 @@ void KMinesMainWindow::setupActions()
     KgDifficultyGUI::init(this);
     connect(Kg::difficulty(), &KgDifficulty::currentLevelChanged, this, &KMinesMainWindow::newGame);
 
-#if QT_VERSION < QT_VERSION_CHECK(5, 14, 0)
-    setupGUI(QApplication::screens().at(0)->availableGeometry().size() * 0.4);
-#else
     setupGUI(screen()->availableGeometry().size() * 0.4);
-#endif
 }
 
 void KMinesMainWindow::onMinesCountChanged(int count)