[cleanup] Remove deprecated dune/common/std/variant.hh

CHANGELOG.md

@@ -57,6 +57,8 @@ In order to build the DUNE core modules you need at least the following software
   objects and `std::function` stuff instead!
 - The deprecated header `dune/common/std/utility.hh` has been removed. Use `<utility>`
   instead.
+- The deprecated header `dune/common/std/variant.hh` has been removed. Use `<variant>`
+  instead.
 
 
 # Release 2.9

dune/common/std/CMakeLists.txt

@@ -7,5 +7,4 @@ install(
   functional.hh
   make_array.hh
   type_traits.hh
-  variant.hh
   DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/dune/common/std)

dune/common/std/variant.hh

-// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
-// vi: set et ts=4 sw=2 sts=2:
-// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
-// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
-#ifndef DUNE_COMMON_STD_VARIANT_HH
-#define DUNE_COMMON_STD_VARIANT_HH
-
-#warning dune/common/std/variant.hh is deprecated and will be removed after Dune 2.8.\
- Include <variant> instead
-
-#include <variant>
-
-namespace Dune {
-namespace Std {
-  using std::variant;
-  using std::visit;
-  using std::variant_size;
-  using std::variant_size_v;
-  using std::get;
-  using std::get_if;
-  using std::holds_alternative;
-  using std::monostate;
-}
-}
-
-#endif