shared: Clean up includes

Split out of #37344.

src/shared/hostname-setup.c

@@ -1,8 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#include <errno.h>
 #include <stdio.h>
-#include <stdlib.h>
 #include <sys/utsname.h>
 #include <unistd.h>
 
@@ -18,7 +16,6 @@
 #include "hostname-util.h"
 #include "initrd-util.h"
 #include "log.h"
-#include "macro.h"
 #include "proc-cmdline.h"
 #include "siphash24.h"
 #include "string-table.h"