Remove redundant includes

These are all included in git-compat-util.h (when necessary), which we
include in cgit.h.

Signed-off-by: John Keeping <john@keeping.me.uk>

shared.c

@@ -7,7 +7,6 @@
  */
 
 #include "cgit.h"
-#include <stdio.h>
 
 struct cgit_repolist cgit_repolist;
 struct cgit_context ctx;