Support for designated revoker?

[kaie]

Does RNP already support designated revokers?
https://www.rfc-editor.org/rfc/rfc4880#section-5.2.3.15

If you don't support it yet, and if you add it in the future, you could consider an exception for
rnp_key_remove_signatures(RNP_KEY_SIGNATURE_NON_SELF_SIG)

I'm guessing that the intention of this constant is to remove unnecessary signatures, to create a minimized key.
However, I think that a revocation signature from an authorized revocation key probably should be kept (treated as a self signature).

[ni4]

@kaie we do not have support for designated revokers yet, this is tracked via the issue #1131
While adding support for it would require some time, initial support for the aforementioned flag may be added first.