[cmake] Remove deprecated DuneCMakeCompat.cmake

CHANGELOG.md

@@ -106,6 +106,9 @@ In order to build the DUNE core modules you need at least the following software
 - Deprecate CMake macro `message_verbose`. Use `message(VERBOSE "message text")` instead.
   This macro will be removed after Dune 2.10.
 
+- Remove deprecated CMake file `DuneCMakeCompat.cmake` that only contained a
+  deprecation message.
+
 - We have changed the way optional dependencies are activated in the build-system internally.
   The cmake macros `add_dune_xy_flags` do not set the compiler flag `-DENABLE_XY=1` anymore, but instead
   set directly the flag `-DHAVE_XY=1`. Neither `ENABLE_XY` nor `HAVE_XY` should be modified manually

cmake/modules/CMakeLists.txt

@@ -20,7 +20,6 @@ install(FILES
   CMakeBuiltinFunctionsDocumentation.cmake
   DuneAddLibrary.cmake
   DuneAddPybind11Module.cmake
-  DuneCMakeCompat.cmake
   DuneCommonMacros.cmake
   DuneDoc.cmake
   DuneDoxygen.cmake

cmake/modules/DuneCMakeCompat.cmake

-# SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
-# SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
-
-# Module with backward compatibility implementation of newer cmake functionality
-message(DEPRECATION "DuneCMakeCompat.cmake file is deprecated. Will be removed after release 2.9")