We started including stdio.h to pick up the declaration of "FILE" in
f26a0012 (Enable wt-status output to a given FILE pointer.,
2007-09-17). But there's no need, since headers can assume that
git-compat-util.h has been included, which covers stdio.

This should just be redundant, and not hurting anything (like pulling in
includes out of order) because C files are supposed to always include
git-compat-util.h first. But it's worth cleaning up to model good
behavior.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>