Rename "Signature Expiration Time" subpacket to "Certification Expiration Time"?

The only concrete use of signature expiration time subpackets is to make certifications time-limited. Binding signatures have key expiration times (and key revocations), and the meaning of document signature expiration times is application-defined (and therefore belongs in the world of notations).

We might wish to deprecate the use of "signature expiration time" outside of certification signatures, and rename it accordingly to hammer home the point.