Remove virtual destructors from POD toolkit types

This one's been haunting me for a couple decades.  "Make all the things
virtual!" was kind of a strategy I had for forward compatibility when I
wrote this code when I was 20 or so and didn't know better.

taglib/fileref.cpp

@@ -299,7 +299,7 @@ public:
     file(nullptr),
     stream(nullptr) {}
 
-  ~FileRefPrivate() override {
+  ~FileRefPrivate() {
     delete file;
     delete stream;
   }