To uninstall darkplaces just follow these instructions.
/debian/stretch/main///install/index.html Game engine for Quake and similar 3D first person shooter games Debian 9.0 games 0~20140513+svn12208-4
sudo apt-get remove darkplaces
Which will remove just the darkplaces package itself.
sudo apt-get remove --auto-remove darkplaces
This will remove the darkplaces package and any other dependant packages which are no longer needed.
If you also want to delete your local/config files for darkplaces then this will work.
sudo apt-get purge darkplaces
Or similarly, like this darkplaces
sudo apt-get purge --auto-remove darkplaces
|Maintainer||Debian Games Team
|Description||Game engine for Quake and similar 3D first person shooter games|