Old removed DDC is listed under Zones (alongside the two current DDCs).
"Get-BrokerController" and database table 'chb_Config.Controllers' shows working DDCs. 

Please always take a backup of database before making any changes.

Manually remove the old DDC entries from the following DB  tables (Site Database):

chb_State.Controller 
ADIdentitySchema.Services
Analytics.Services
AppLibrarySchema.Services
ConfigLoggingSiteSchema.Services 
ConfigurationSchema.Services
DAS.Services
DesktopUpdateManagerSchema.Services
EnvTestServiceSchema.Services
HostingUnitServiceSchema.Services 
Monitor.Services 
OrchestrationSchema.Services 
TrustSchema.Services 
StorefrontSchema.Services 

Problem Cause

Old DDC entry was present in the Database in the following tables 

chb_State.Controller 
ADIdentitySchema.Services
Analytics.Services
AppLibrarySchema.Services
ConfigLoggingSiteSchema.Services 
ConfigurationSchema.Services
DAS.Services
DesktopUpdateManagerSchema.Services
EnvTestServiceSchema.Services
HostingUnitServiceSchema.Services 
Monitor.Services 
OrchestrationSchema.Services 
TrustSchema.Services 
StorefrontSchema.Services  

You can also use stored procedures:

https://support.citrix.com/s/article/CTX225347-how-to-evict-a-ddc-using-tsql?language=en_US

Evict script:

https://support.citrix.com/s/article/CTX232985-how-to-build-an-evict-script?language=en_US