ovmerge: Update Copyright details, remove GPL-2.0

The BSD 3-Clause licence is sufficiently permissive that a dual licence
with GPL-2.0 shouldn't add anything. Revert to BSD3 to match everything
else in this repo, and update the Copyright message, which has fallen
behind recent changes.

Signed-off-by: Phil Elwell <[email protected]>

Author: pelwell

ovmerge/ovmerge

@@ -1,7 +1,7 @@
 #!/usr/bin/perl
 
 # Author: Phil Elwell <[email protected]>
-# Copyright (c) 2018-2021, Raspberry Pi (Trading) Ltd.
+# Copyright (c) 2018-2025, Raspberry Pi Ltd.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
@@ -16,10 +16,6 @@
 #    to endorse or promote products derived from this software without
 #    specific prior written permission.
 #
-# ALTERNATIVELY, this software may be distributed under the terms of the
-# GNU General Public License ("GPL") version 2, as published by the Free
-# Software Foundation.
-#
 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 # IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 # THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR