proto/soru: remove dead refutation games at migration

Context

If two players involved in a refutation game where both were slashed, they have no incentive to finish the refutation game. We do it for them to clean the storage.

Manually testing the MR

Play with migrate_from migrate_to framework in tezt

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR