This page:
is most interesting. But when you have just started adsiedit (which has to be started from an administrator console!), you won’t see anything, until you right-click on the object, click on Connect To, and choose “Select a well known Naming Context”, open the dropdown, and choose “Configuration”. Then you go here:
CN=Configuration,
CN=Services,
CN=Microsoft Exchange,
CN=[YourExchangeOrganisationName],
CN=Administrative Groups,
CN=[LegacyAdministrativeGroupName],
CN=Servers
and delete the “Servers” container. Then restart the Microsoft Exchange Active Directory Topology service, and you are done.