Remove duration from serializer.
Remove duration from serializer.

City-of-Helsinki/linkedevents,tuomas777/linkedevents,kooditiimi/linkedevents,aapris/linkedevents,tuomas777/linkedevents,aapris/linkedevents,kooditiimi/linkedevents,tuomas777/linkedevents,aapris/linkedevents,kooditiimi/linkedevents,City-of-Helsinki/linkedevents,City-of-Helsinki/linkedevents,kooditiimi/linkedevents