So a client decommissioned several DHCP servers improperly. So every time you opened the DHCP Console, it displayed those servers even though they have been gone for some time now.
Connect to the configuration container
navigate to CN=configuration,CN=Services,cn=Netservices
In the right pane, Double-click the CN=DHCPROOT entry
Find dhcpServers, remove the names of the decommisioned servers.