Why would you submit a PR to not create them? Simply because you don't use them, and break it for a lot of other users?
They are used/required by the Opauth component of Auth. The migrations can't smell you are not going to use that component. The user roles table is also not needed if your access system doesn't use roles.
If you don't use those tables, nobody is stopping you from adding a migration to your app that deletes them, and creates them again in your down migration. It is the most clear solution.
This was the part which was not obvious to me. That, and I don't understand the difference between Opauth and OAuth. I had to ask, anyways. The simpleauth schema was too complicated and feature rich for our basic use here.
I hoped to avoid writing a down migration to re-create those tables, so I've decided to document them as database-padding instead. ;)