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/playlist/playlistdelegates.cpp

@@ -172,11 +172,7 @@ QString PlaylistDelegateBase::displayText(const QVariant &value, const QLocale&)
 
   QString text;
 
-#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
   switch (value.metaType().id()) {
-#else
-  switch (static_cast<QMetaType::Type>(value.type())) {
-#endif
     case QMetaType::Int:{
       int v = value.toInt();
       if (v > 0) text = QString::number(v);
@@ -441,11 +437,7 @@ QString NativeSeparatorsDelegate::displayText(const QVariant &value, const QLoca
   const QString string_value = value.toString();
 
   QUrl url;
-#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
   if (value.metaType().id() == QMetaType::QUrl) {
-#else
-  if (value.type() == QVariant::Url) {
-#endif
     url = value.toUrl();
   }
   else if (string_value.contains(QLatin1String("://"))) {
@@ -478,11 +470,7 @@ QPixmap SongSourceDelegate::LookupPixmap(const Song::Source source, const QSize
   }
 
   QIcon icon(Song::IconForSource(source));
-#if (QT_VERSION >= QT_VERSION_CHECK(6, 0, 0))
   pixmap = icon.pixmap(size, device_pixel_ratio);
-#else
-  pixmap = icon.pixmap(size);
-#endif
   QPixmapCache::insert(pixmap_cache_key, pixmap);
 
   return pixmap;