Remove support for deprecated IPNS records v1

[lidel]

Part of ipfs/specs#314, corresponding JS-IPFS issue: ipfs/js-ipfs#4197

Support for extensible records (and v2 signature) was added in 2021. Kubo is producing and preferring updated v2 IPNS records by default, but if no v2 is found, it will still accept deprecated v1 for backward-compatibility during the transition period.

A year later, we should remove fallback support for validating v1 signatures and ignore them instead.