Personally my count was 22. Maybe I was counting something other people weren't (Nagash, the Charnel Throne, or maybe Royal Beastflayers), or maybe I just made a miscount.
If there was a single unit that was getting removed, honestly I'd say it would be the Crypt Ghast Courtier. It looks exactly the same as a Crypt Ghast, as opposed to the Crypt Haunter Courtiers and Crypt Infernal Courtiers who have their own little conversions to make them unique (Crypt Haunter having a Vargheist head while Crypt Infernal has the extra set of wings from the Vargheist champion). Plus, recently GW has been doing a thing where if a kit can make a single model into a hero they let you take a single instance of that unit under-strength as compensation, and it would probably be more elegant to have 2-man Crypt Horrors or Crypt Flayers instead of 19 man Ghouls.