Stop putting `actor` on non-Activity objects
https://www.w3.org/TR/activitystreams-vocabulary/#dfn-actor
The actor
property's domain is Activity, so it is only valid on activities. It should be removed from the Object representation of posts.
I haven't verified whether activities produced by Pleroma use both actor
and attributedTo
in the same way that objects do, but if so, then they should remove attributedTo
as well.