Revert r327005 - SPDX tags for license similar to BSD-2-Clause.

After consultation with SPDX experts and their matching guidelines[1],
the licensing doesn't exactly match the BSD-2-Clause. It yet remains to be
determined if they are equivalent or if there is a recognized license that
matches but it is safer to just revert the tags.

Let this also be a reminder that on FreeBSD, SPDX tags are only advisory
and have no legal value (but IANAL).

Pointyhat to:	pfg
Thanks to:	Rodney Grimes, Gary O'Neall

[1] https://spdx.org/spdx-license-list/matching-guidelines

sbin/ipfw/altq.c

@@ -1,6 +1,4 @@
 /*-
- * SPDX-License-Identifier: BSD-2-Clause
- * 
  * Copyright (c) 2002-2003 Luigi Rizzo
  * Copyright (c) 1996 Alex Nash, Paul Traina, Poul-Henning Kamp
  * Copyright (c) 1994 Ugen J.S.Antsilevich

sbin/ipfw/dummynet.c

@@ -1,6 +1,4 @@
-/*.
- * SPDX-License-Identifier: BSD-2-Clause
- * 
+/*-
  * Codel/FQ_Codel and PIE/FQ_PIE Code:
  * Copyright (C) 2016 Centre for Advanced Internet Architectures,
  *  Swinburne University of Technology, Melbourne, Australia.

sbin/ipfw/ipfw2.c

@@ -1,6 +1,4 @@
 /*-
- * SPDX-License-Identifier: BSD-2-Clause
- * 
  * Copyright (c) 2002-2003 Luigi Rizzo
  * Copyright (c) 1996 Alex Nash, Paul Traina, Poul-Henning Kamp
  * Copyright (c) 1994 Ugen J.S.Antsilevich

sbin/ipfw/ipfw2.h

@@ -1,6 +1,4 @@
 /*-
- * SPDX-License-Identifier: BSD-2-Clause
- * 
  * Copyright (c) 2002-2003 Luigi Rizzo
  * Copyright (c) 1996 Alex Nash, Paul Traina, Poul-Henning Kamp
  * Copyright (c) 1994 Ugen J.S.Antsilevich

sbin/ipfw/ipv6.c

@@ -1,6 +1,4 @@
 /*-
- * SPDX-License-Identifier: BSD-2-Clause
- * 
  * Copyright (c) 2002-2003 Luigi Rizzo
  * Copyright (c) 1996 Alex Nash, Paul Traina, Poul-Henning Kamp
  * Copyright (c) 1994 Ugen J.S.Antsilevich

sbin/ipfw/main.c

@@ -1,6 +1,4 @@
 /*-
- * SPDX-License-Identifier: BSD-2-Clause
- * 
  * Copyright (c) 2002-2003,2010 Luigi Rizzo
  * Copyright (c) 1996 Alex Nash, Paul Traina, Poul-Henning Kamp
  * Copyright (c) 1994 Ugen J.S.Antsilevich

sbin/ipfw/nat.c

@@ -1,6 +1,4 @@
 /*-
- * SPDX-License-Identifier: BSD-2-Clause
- * 
  * Copyright (c) 2002-2003 Luigi Rizzo
  * Copyright (c) 1996 Alex Nash, Paul Traina, Poul-Henning Kamp
  * Copyright (c) 1994 Ugen J.S.Antsilevich

sys/sys/msg.h

@@ -6,8 +6,6 @@
  *
  * Author:  Daniel Boulet
  *
- * SPDX-License-Identifier: BSD-2-Clause
- *
  * Copyright 1993 Daniel Boulet and RTMX Inc.
  *
  * This system call was implemented by Daniel Boulet under contract from RTMX.

sys/sys/snoop.h

@@ -1,6 +1,4 @@
 /*-
- * SPDX-License-Identifier: BSD-2-Clause
- *
  * Copyright (c) 1995 Ugen J.S.Antsilevich
  *
  * Redistribution and use in source forms, with and without modification,

usr.sbin/watch/watch.c

@@ -1,6 +1,4 @@
 /*-
- * SPDX-License-Identifier: BSD-2-Clause
- *
  * Copyright (c) 1995 Ugen J.S.Antsilevich
  *
  * Redistribution and use in source forms, with and without modification,