tree-wide: drop several remaining license headers

And downgrade the license of utf8.c to LGPL-2.0-or-later, to follow the
original license.

src/shared/initreq.h

@@ -1,14 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.0-or-later */
 /*
- * initreq.h	Interface to talk to init through /dev/initctl.
- *
- *		Copyright (C) 1995-2004 Miquel van Smoorenburg
- *
- *		This library is free software; you can redistribute it and/or
- *		modify it under the terms of the GNU Lesser General Public
- *		License as published by the Free Software Foundation; either
- *		version 2 of the License, or (at your option) any later version.
- *
+ * Copyright (C) 1995-2004 Miquel van Smoorenburg
  * Version:     @(#)initreq.h  1.28  31-Mar-2004 MvS
  */