GC stores rider related information in 2 places
- Athlete Subdirectory - all the rides files, most configuration XML files, ...
If you remove the Athlete Subdirectory/Folder the Athlete will not appear in GC's list any more. So this will do the main job.
The number of "other settings" is considerably small. If you want to clean them you need the knowledge on the OS. E.g. on Windows you need to go to the registry (regedit.exe) and search for GoldenCheetah - then you also find you athletes as sub-trees in the registry structure. Editing such settings is more critical - if you delete the wrong part ..... - so on your own risk.
Joern