Repository cleanup: removed affixes from cs:et-al

Just a note that I deleted any affixes (cs:prefix and cs:suffix) from
cs:et-al for the repository styles. As far as I know they never did
anything in citeproc-js, they were explicitly deprecated in CSL 1.0.1,
and CSL 1.0.1 introduced the delimiter-precedes-et-al attribute to
control the delimiter between the last name and the “et-al” term. See