ActivityPub: Don't mention people on private posts
Hubzilla currently tags accounts on private posts. This is done since Hubzilla currently doesn't display private postings when this isn't done.
But this does have a downside: On Mastodon these posts arrive in the wrong timeline and users are notified about every single post. Same will happen with the upcoming AP integration in Friendica and surely many more AP implementations.
I opened an issue at Mastodon for this: https://github.com/tootsuite/mastodon/issues/8752