Revert "musl: utmpx: add several missing definitions"

This reverts commit 3ae7d8fd87.

Now utmp support is always disabled when building with musl,
and all definitions are unused in that case. Let's remove it.

src/include/musl/utmpx.h

@@ -1,16 +0,0 @@
-/* SPDX-License-Identifier: LGPL-2.1-or-later */
-#pragma once
-
-#include_next <utmpx.h>
-
-#ifndef UTMPX_FILE
-#define UTMPX_FILE "/run/utmp"
-#endif
-
-#ifndef WTMPX_FILE
-#define WTMPX_FILE "/var/log/wtmp"
-#endif
-
-#ifndef ACCOUNTING
-#define ACCOUNTING 9
-#endif