This is part of deprecation described in ipfs/kubo#9240
- record creation continues to create both V1 and V2  signatures
- record validation no longer accepts V1 signatures

Meaning:
- modern nodes are 100% V2, they ignore V1 signatures
- legacy nodes (go-ipfs < v0.9.0) are still able to resolve names
  created by go-ipns, because V1 is still present

This is a PoC that shows minimal set of changes to allow "pure V2" IPNS
records which have only two protobuf fields: `IpnsEntry.Data` and
`IpnsEntry.SignatureV2`

`Create` still creates V1+V2, but the `Validate` only cares about V2
fields.

Makes it more clear when we require CBOR to match protobuf