Copyright.txt: Drop outdated content around copyright notice line

The modern convention for BSD 3-Clause license notices does not
include the name of the project or "All rights reserved".

Copyright.txt

@@ -1,6 +1,4 @@
-CMake - Cross Platform Makefile Generator
 Copyright 2000-2025 Kitware, Inc. and Contributors
-All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions