If the Domain Controller is running locally the AD Connector, you need to remove both entries from the dashboard. And if you have other AD connectors in your deployment, restart the service.
When a VA or Connector is installed, it registers a corresponding object to the dashboard under:
-->settings -->Sites and Active Directory
The Domain Controller configuration script also registers each DC it is run on to the dashboard.
All of these objects can be deleted. It is worth noting that this is also where 'Umbrella Sites' can be created, and where the Insights components are divided into these sites, so if you are removing on a site-by-site basis, ensure you only delete the components that are assigned to that site.
