This feature was both conceptually broken and through bitrotting
the implementation was also buggy with the handling of certain
list-post interactions just crashing.
Remote servers had no way to know who belongs to a list and thus
posts basically showed just up as weird DM threads with different
participants on each instance. And while on the local instance
addition and removal from a listed grated and revoked post
access retroactively, it never acted retroactively on remotes.
Notably our "activity_visibility" database function also didn’t
know about "list visibility" instead treating them as direct messages.
Furthermore no known client actualy allows creating such messages
and the lack of complaints about the accumulutaed bugs supports
the absence of any users.
Given this there seems no point in fixing the implementation.
To reduce complexity of visibility handling it will be dropped instead.
Note, a similar effect with less federation weirdness can already be achieved
client-side using the explicit-addressing feature originally introduced in
https://git.pleroma.social/pleroma/pleroma/-/merge_requests/1239.
Ref: https://akkoma.dev/AkkomaGang/akkoma/issues/812
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