Followers-only posts and DMs went to each recipient's personal inbox,
so a followers-only post was sent once per follower on the same server.
Mastodon, GoToSocial and Iceshrimp.NET always use the shared inbox.
Only activities with bcc or bto still go to personal inboxes.
Based on Akkoma a80444041.
Co-authored-by: Oneric <oneric@oneric.stub>
