Find all tasks associated to users

I have an issue with duplicate users in our system.   My goal is to find all the users who do not have any tasks, CIs, Approvals, etc tied to them and delete those users.   Then, I will configure our coalesce to work accurately based on the systems we import from.

I've search the Wiki and Community, but haven't found anything that will tell me how to find these users.   Any help will be much appreciated!