Currently on pypi-legacy, it's possible for a user to have both the "Owner" and "Maintainer" roles.

However, an "Owner" can do everything a "Maintainer" can do, so it doesn't make sense for a user to be able to have both roles.

In the short term, we decided to add a hack to hide any "duplicate" roles in #2705, and remove the ability to add multiple roles for the same user in Warehouse.

Once pypi-legacy is shut down, we can run a migration which removes any of these "duplicate" roles., and remove this hack.