retire phplist

[irabinovitch]

I believe we're done with phplist and moved entirely to listmonk. we can probably remove phplist from chef, and complete the list migration to centos10. we should also kill the phplist rds cluster after backup.

[jaymzh]

It cannot be shutdown - it still runs mailman.

[irabinovitch]

I thought we had 2 machines up for this one for the new mailman and one for phplist. Apparently my memory was off and after reinventorying i see you just kept the centos9 list box so we could keep phplist around. We no longer need phplist, so if you'd like to complete that upgrade I guess we're unblocked now.

When we're done with that, we can probably shutdown the phplist rds cluster after a backup/snapshot too to save a bit more there as well.

[irabinovitch]

I've updated the description and title to match.