test-hashmap.c: drop unnecessary #includes

Per Documentation/CodingGuidelines most C files in git start with
a #include of git-compat-util.h or another header file that includes
it, such as cache.h or builtin.h.  This file doesn't need anything
beyond "git-compat-util.h", so use that.

Remove a #include of the system header <stdio.h> since it is already
included by "git-compat-util.h".
Signed-off-by: NJonathan Nieder <jrnieder@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

test-hashmap.c

-#include "cache.h"
+#include "git-compat-util.h"
 #include "hashmap.h"
-#include <stdio.h>
 
 struct test_entry
 {