basic + fundamental: Clean up includes

Split out of #37344.

src/basic/io-util.c

@@ -1,14 +1,13 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#include <errno.h>
-#include <limits.h>
+#include <poll.h>
 #include <stdio.h>
+#include <string.h>
+#include <time.h>
 #include <unistd.h>
 
 #include "errno-util.h"
 #include "io-util.h"
-#include "iovec-util.h"
-#include "string-util.h"
 #include "time-util.h"
 
 int flush_fd(int fd) {