spdx: The BSD-2-Clause-NetBSD identifier is obsolete, drop -NetBSD

The SPDX folks have obsoleted the BSD-2-Clause-NetBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with:		pfg
MFC After:		3 days
Sponsored by:		Netflix

libexec/rpc.sprayd/sprayd.c

@@ -1,7 +1,7 @@
 /*	$NetBSD: sprayd.c,v 1.15 2009/10/21 01:07:46 snj Exp $	*/
 
 /*-
- * SPDX-License-Identifier: BSD-2-Clause-NetBSD
+ * SPDX-License-Identifier: BSD-2-Clause
  *
  * Copyright (c) 1994 Christos Zoulas
  * All rights reserved.

libexec/rtld-elf/powerpc/reloc.c

@@ -1,7 +1,7 @@
 /*      $NetBSD: ppc_reloc.c,v 1.10 2001/09/10 06:09:41 mycroft Exp $   */
 
 /*-
- * SPDX-License-Identifier: BSD-2-Clause-NetBSD
+ * SPDX-License-Identifier: BSD-2-Clause
  *
  * Copyright (C) 1998   Tsubai Masanari
  * All rights reserved.

libexec/rtld-elf/powerpc64/reloc.c

@@ -1,7 +1,7 @@
 /*      $NetBSD: ppc_reloc.c,v 1.10 2001/09/10 06:09:41 mycroft Exp $   */
 
 /*-
- * SPDX-License-Identifier: BSD-2-Clause-NetBSD
+ * SPDX-License-Identifier: BSD-2-Clause
  *
  * Copyright (C) 1998   Tsubai Masanari
  * All rights reserved.