ref-filter: mark unused parameters in parser callbacks

ref-filter: mark unused parameters in parser callbacks

These are similar to the cases annotated in 5fe9e1ce2f (ref-filter: mark
unused callback parameters, 2023-02-24), but were added after that
commit.

Note that the ahead/behind callback ignores its "atom" parameter, which
is a little unusual, since that struct usually stores the result. But in
this case, the data is stored centrally in ref_array->counts, since we
want to compute all ahead/behinds at once, not per ref.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>