tl;dr: restart SMS_SITE_COMPONENT_MANAGER service through Configuration Manager Service Manager
After uninstalling a SUP from a Site Server, the Component Server Role was not disappearing from the roles-listing of the old site system.
After searching a while I found this blogpost for the 2007 SCCM environment. It also works in an 2012SP1 environment:
1. In your SCCM Console open Monitoring and choose site status.
2. look for a component server an right click it. Select Start –> Configuration Manager Service Manager
3. In the service Manager, expand a working server and navigate to SMS_SITE_COMPONENT_MANAGER
4. Select SMS_SITE_COMPONENT_MANAGER and right click it. Select query. After a short time you will get the recent service status.
5. now you can stop the service: right click it and select stop service
6. query the service again
7. start the service: rights click and start service
8. Take a look in your site administration: the Component Server role should be gone
Hope that helps