5.6betaのリリースノートから引用

Server App
With this release of macOS Server 5.6, we are deprecating the open source servers we
redistribute as part of Server (Open Directory, the Calendar Server, the Contacts Server, and
the Mail Server, DNS, DHCP, VPN Server, and Websites). New installations of this version will
not show those services in the sidebar of Server.app, but if you are upgrading, any services
which are already enabled will still be visible in the sidebar.
With the Fall 2018 macOS Server release, we will stop re-distributing open source servers
(Open Directory, the Calendar Server, the Contacts Server, and the Mail Server, DNS, DHCP,
VPN Server, and Websites). For more information, please refer to:
https://support.apple.com/
en-us/HT208312
.
We continue to actively develop and support the other features of macOS
Server, including
Open Directory, Profile Manager and Xsan management

今有効にしているモノは5.6でも有効だけどそれ以外は消える（モノが？それとも設定だけ？）みたい
しかしそれも一時的で
秋にはなんとopendirectoryも含め！ほとんど削除になるみたいね