When trying to delete a provisioning role in Identity Manager, you see the following error:
Error: Task failed.
Error: You can not delete a provisioning role that contains members. Return to search and uncheck the roles shown below from the delete list.
Error: 'ROLE NAME' contains members and can not be deleted.
To remove all users you need to go to Provisioning Manager -> Roles -> look up the role -> Right click, list global users -> remove it from all users. Once the role no longer shows any users through this method, it will delete without errors.