Remove legacy element serializer (#1810)
Remove legacy element serializer (#1810)

This serializer has been introduced 4 years ago with the release of
Alchemy 3.1. This can be safely removed now.
robinboening/alchemy_cms,AlchemyCMS/alchemy_cms,robinboening/alchemy_cms,mamhoff/alchemy_cms,AlchemyCMS/alchemy_cms,mamhoff/alchemy_cms,mamhoff/alchemy_cms,AlchemyCMS/alchemy_cms,robinboening/alchemy_cms