remove unused includes

This patch removes includes that are not used. The removals were found with
include-what-you-use which checks if any of the symbols from a header is
in use.

src/shared/json.c

@@ -23,7 +23,6 @@
 #include <math.h>
 
 #include "macro.h"
-#include "log.h"
 #include "util.h"
 #include "utf8.h"
 #include "json.h"