basic: include only what we use

This is a cleaned up result of running iwyu but without forward
declarations on src/basic.

src/basic/audit-util.c

@@ -20,7 +20,9 @@
 ***/
 
 #include <errno.h>
+#include <linux/netlink.h>
 #include <stdio.h>
+#include <sys/socket.h>
 
 #include "alloc-util.h"
 #include "audit-util.h"
@@ -30,7 +32,6 @@
 #include "parse-util.h"
 #include "process-util.h"
 #include "user-util.h"
-#include "util.h"
 
 int audit_session_from_pid(pid_t pid, uint32_t *id) {
         _cleanup_free_ char *s = NULL;