Benefits: Revoke upon one-time purchase refunds

[birkjernstrom]

Context

We automatically revoke benefits on subscription revokation. However, since one-time purchases are meant to be "lifetime" we don't revoke any benefits for them, but that's also because we don't offer automation for refunds (yet) where it would make sense.

Goal

Upon refunds of one-time purchases, revoke all benefits for one-time purchases. Unless our future refunds object allows for explicitly keeping them.