This is so that multiple users can be paired with a single list.
In the future, we may want to reconsider list deletion behavior to simply remove a user's access and only delete it when no one has access.
We may also want the user deletion Lambda to use the list deletion Lambda when it is created.
Prototype the User DELETE lambda. Amplify does not include this functionality, so putting it in a Lambda with the fine-grained API. This currently does not invalidate outstanding tokens nor does it clean up the database.
@claytonwwilson You will want to add the clean up code instead of the deleted stuff in UserDeleter
