Revert "Fix failing tests by avoiding prefetch"

This reverts commit bd065b88.

api/funkwhale_api/music/serializers.py

@@ -230,7 +230,7 @@ class TrackAlbumSerializer(serializers.ModelSerializer):
     tracks_count = serializers.SerializerMethodField()
 
     def get_tracks_count(self, o):
-        return len(o.tracks.all())
+        return getattr(o, "_prefetched_tracks_count", 0)
 
     class Meta:
         model = models.Album