Orphaned Custom Roles

I tested this plugin a few years back. Today I was preparing to add some additional user roles and see there are still a few orphaned items left by All-in-One Event Calendar. Specifically there is a custom user role named “Event Contributor (ai1ec_event_assistant)” still active. I don’t see were this is stored and I would like to remove it. I’ve searched the DB, and looked thru my parent and child theme functions.