common/crypto/signature: Use a newer version of ECVRF

[Yawning]

When I implemented ECVRF in curve25519-voi, the IETF draft was less than version 11. As of version 11, after leaving things largely unchanged for years, they broke proof backward compatibility.

• [x] The next time we bump the curve25519-voi import, switch to using the v10 backward compatible proof/verify routines. (#4839)
• [ ] Whenever we can jettison beacon state (so a dump-restore hard fork) switch to using the v13 style proofs.

[Yawning]

https://github.com/oasisprotocol/curve25519-voi/pull/114