Based on the responses in a feature request, the best way to remove older ruby versions is to go back to the src directory and run make uninstall or rake uninstall. By default, ruby-install uses $HOME/src/ruby-$version for unpacked sources of ruby versions during installation.

The next viable way is to use Adobe CC Cleaner tool - which is not publically advertised. If anyone reading this is facing the problem I have described above, download the CC Cleaner Tool here: https://helpx.adobe.com/creative-cloud/kb/cc-cleaner-tool-installation-problems.html