wt-status.h: drop stdio.h include

We started including stdio.h to pick up the declaration of "FILE" in f26a001226 (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: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>