commit-graph: stop using optname()

commit-graph: stop using optname()

Stop using optname() in builtin/commit-graph.c to emit an error with
the --max-new-filters option. This changes code added in 809e0327f57
(builtin/commit-graph.c: introduce '--max-new-filters=<n>',
2020-09-18).

See 9440b831ad5 (parse-options: replace opterror() with optname(),
2018-11-10) for why using optname() like this is considered bad,
i.e. it's assembling human-readable output piecemeal, and the "option
`X'" at the start can't be translated.

It didn't matter in this case, but this code was also buggy in its use
of "opt->flags" to optname(), that function expects flags, but not
*those* flags.

Let's pass "max-new-filters" to the new error because the option name
isn't translatable, and because we can re-use a translation added in
f7e68a08780 (parse-options: check empty value in OPT_INTEGER and
OPT_ABBREV, 2019-05-29).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>