Remove all uses of QTextCodec

src/core/song.h

@@ -38,7 +38,6 @@
 #include <QImage>
 #include <QIcon>
 
-class QTextCodec;
 class QSqlQuery;
 
 namespace Engine {
@@ -177,8 +176,6 @@ class Song {
   // Useful when you want updated tags from disk but you want to keep user stats.
   void MergeUserSetData(const Song &other);
 
-  static QString Decode(const QString &tag, const QTextCodec *codec = nullptr);
-
   // Save
   void BindToQuery(QSqlQuery *query) const;
   void BindToFtsQuery(QSqlQuery *query) const;