basic + fundamental: Clean up includes

Split out of #37344.

src/basic/env-file.h

@@ -1,11 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
-#include <fcntl.h>
-#include <stdarg.h>
-#include <stdio.h>
-
-#include "macro.h"
+#include "forward.h"
 
 int parse_env_filev(FILE *f, const char *fname, va_list ap);
 int parse_env_file_fdv(int fd, const char *fname, va_list ap);