Remove site server from ConfigMgr
All site system roles except for the Distribution Point role will also add the “Component Server” role in ConfigMgr. This role is supposed to automatically uninstall itself after all dependent roles are removed. Sometimes, when decommissioning a server, this does not happen. To force it, simply open the Site Server role and change ANY setting. Obviously the most easy to change is the one about site server connections. Just change any setting and save it. Within a few minutes, the Component Server role will disappear and you can delete the site system.