*.c static functions: don't forward-declare __attribute__

*.c static functions: don't forward-declare __attribute__

9cf6d3357aa (Add git-index-pack utility, 2005-10-12) and
466dbc42f58 (receive-pack: Send internal errors over side-band #2,
2010-02-10) we added these static functions and forward-declared their
__attribute__((printf)).

I think this may have been to work around some compiler limitation at
the time, but in any case we have a lot of code that uses the briefer
way of declaring these that I'm using here, so if we had any such
issues with compilers we'd have seen them already.

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