Initial iteration for Qt6 port.

src/SeerMainWindow.cpp

@@ -13,7 +13,6 @@
 #include <QtGui/QPalette>
 #include <QtCore/QCoreApplication>
 #include <QtCore/QTimer>
-#include <QtCore5Compat/QRegExp>
 #include <QRegularExpression>
 #include <QtCore/QSettings>
 #include <QtCore/QDebug>
@@ -55,11 +54,7 @@ SeerMainWindow::SeerMainWindow(QWidget* parent) : QMainWindow(parent) {
 
     // Set up Styles menu.
     _styleMenuActionGroup = new QActionGroup(this);
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 14, 0))
     _styleMenuActionGroup->setExclusionPolicy(QActionGroup::ExclusionPolicy::Exclusive);
-#else
-    _styleMenuActionGroup->setExclusive(true);
-#endif
     _styleMenuActionGroup->setEnabled(true);
     _styleMenuActionGroup->setVisible(true);