Retire affixes on cs:et-al

A user recently reported that citeproc-js ignores affixes on cs:et-al, even
though they allowed by the CSL 1.0 spec. I tried tracking down why we allow
affixes on cs:et-al in the first place, and it seems to be a left-over from
a time where we contemplated using the “prefix” attribute to control the
delimiter between the last name and et-al. However, we ended up introducing
the delimiter-precedes-et-al attribute. As such, I think we can safely do
without affixes on cs:et-al.

If there are no objections, I would like to retire “prefix” and “suffix” on
cs:et-al. Affixes would no longer be mentioned in the spec in the
description of cs:et-al, and I would mark the attributes as “legacy” in the
schema to prevent backwards-incompatibility.


citeproc-js ticket:
the introduction of cs:et-al:
the introduction of delimiter-precedes-et-al:

All good for me.