ObjectView: do not fetch an object for its ID

ObjectView: do not fetch an object for its ID

Non-Create/Listen activities had their associated object field
normalized and fetched, but only to use their `id` field, which is both
slow and redundant. This also failed on Undo activities, which delete
the associated object/activity in database.

Undo activities will now render properly and database loads should
improve ever so slightly.