Remove cxx feature checks that are already in c++17 standard library
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This MR removes some c++ feature checks from cmake, since the features are already standard:
DUNE_HAVE_CXX_BOOL_CONSTANTDUNE_HAVE_CXX_EXPERIMENTAL_BOOL_CONSTANTDUNE_HAVE_HEADER_EXPERIMENTAL_TYPE_TRAITSDUNE_HAVE_CXX_APPLYDUNE_HAVE_CXX_EXPERIMENTAL_APPLYHAVE_IS_INDEXABLE_SUPPORTThe fallback implementations are removed and the inclusion into the Dune::Std namespace is marked deprecated. This does typically not work for using declarations. Thus, the functions are marked deprecated in Doxygen only.