Servers controller and view allow type LDAP

The Server controller/view at /registry/servers/add/co:N allows the user to choose type "LDAP" but the code for that type is not part of the 4.0.x series.

Benn writes in Slack "The LdapServer refactoring was never finished in the v4 series. (It’ll be done for v5, but at this point probably not worth retrofitting v4 unless we need to for Transmogrification.) It looks like it was at some point committed to the ServerEnum, we should probably just comment that out in Server.php, enum.php, and lang.php."