Drop Qt 5 support

Qt 6 has been available for almost 4 years. Qt 5 is no longer officially supported by Qt for opensource, it's time to drop Qt 5.

src/dialogs/edittagdialog.cpp

@@ -326,11 +326,7 @@ bool EditTagDialog::eventFilter(QObject *o, QEvent *e) {
       case QEvent::MouseButtonRelease:{
         QMouseEvent *mouse_event = static_cast<QMouseEvent*>(e);
         if (mouse_event && mouse_event->button() == Qt::RightButton) {
-#if (QT_VERSION >= QT_VERSION_CHECK(6, 0, 0))
           cover_menu_->popup(mouse_event->globalPosition().toPoint());
-#else
-          cover_menu_->popup(mouse_event->globalPos());
-#endif
         }
         break;
       }

src/dialogs/messagedialog.cpp

@@ -54,11 +54,7 @@ void MessageDialog::ShowMessage(const QString &title, const QString &message, co
   setWindowTitle(title);
 
   if (!icon.isNull()) {
-#if (QT_VERSION >= QT_VERSION_CHECK(6, 0, 0))
     const QPixmap pixmap = icon.pixmap(QSize(64, 64), devicePixelRatioF());
-#else
-    const QPixmap pixmap = icon.pixmap(QSize(64, 64));
-#endif
     ui_->label_logo->setPixmap(pixmap);
   }
 

src/dialogs/snapdialog.cpp

@@ -30,11 +30,7 @@ SnapDialog::SnapDialog(QWidget *parent) : MessageDialog(parent) {
   setWindowTitle(tr("Strawberry is running as a Snap"));
 
   const QIcon icon = IconLoader::Load(QStringLiteral("dialog-warning"));
-#if (QT_VERSION >= QT_VERSION_CHECK(6, 0, 0))
   const QPixmap pixmap = icon.pixmap(QSize(64, 64), devicePixelRatioF());
-#else
-  const QPixmap pixmap = icon.pixmap(QSize(64, 64));
-#endif
   ui_->label_logo->setPixmap(pixmap);
 
   QString text;