Remove default known notations

[twiss]

Since we don't interpret these notations, it is up to the caller to handle them, and thus also to decide whether they are "known". If they are marked as critical, and aren't handled by the caller, we should consider the signature unverified.

Though these notations don't seem super security-critical, it's not up to us to decide, the signer shouldn't mark them as critical if they don't want the signature to fail if we don't interpret them.

Cc @wiktor-k, let me know if you disagree, since you originally added this, but I think it was based on my suggestion, that I now think was mistaken :)

[larabr]

Maybe we can improve the explanation of the field since we are at it, e.g. clarify we're talking about signature validation. And that unsigned notations are ignored (idk if it's obvious)

[wiktor-k]

I'm ok with this change. I think I copied them from Gnupg's default list but since OpenPGP.js is not an end user app in itself I think your change has merit 👍

[twiss]

Maybe we can improve the explanation of the field since we are at it, e.g. clarify we're talking about signature validation. And that unsigned notations are ignored (idk if it's obvious)

To be honest, since the only case where people are likely to need to use or look at this config value is when a signature fails to verify, I think it's somewhat obvious. Ofc we can always improve it but I'll leave it for another PR 😊