I had both Chrome and Chromium installed - CCleaner found Chrome and allowed me to uninstall.
CCleaner did not inventory Chromium (installed to C:\Users\<user>\AppData\Local\chromium) and as a result is not showing as an app that can be uninstalled.
Because it under my profile, I can manually delete it but should this app been recognized in the inventory scan?
If Chromium doesn't appear in the Windows Programs and Features uninstall list, you can manually delete its registry info and files from the PC.
Since uninstalling it normally didn't work you could try to use a powerful uninstall program like Revo Uninstaller to try and force it off of your computer. If that fails I would use a more powerful anti-virus program like Malwarebytes and see if that turns up anything.