drop unused argc parameters

drop unused argc parameters

Many functions take an argv/argc pair, but never actually look at argc.
This makes it useless at best (we use the NULL sentinel in argv to find
the end of the array), and misleading at worst (what happens if the argc
count does not match the argv NULL?).

In each of these instances, the argv NULL does match the argc count, so
there are no bugs here. But let's tighten the interfaces to make it
harder to get wrong (and to reduce some -Wunused-parameter complaints).

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