[cleanup] Remove usage of Dune::Conversion<T1,T2>::exists and remove test for it

dune/common/test/CMakeLists.txt

@@ -38,8 +38,6 @@ dune_add_test(SOURCES classnametest.cc
 dune_add_test(SOURCES concept.cc
               LINK_LIBRARIES dunecommon)
 
-dune_add_test(SOURCES conversiontest.cc)
-
 dune_add_test(SOURCES diagonalmatrixtest.cc
               LINK_LIBRARIES dunecommon)
 

dune/common/test/Makefile.am

@@ -8,7 +8,6 @@ TESTPROGS = \
     calloncetest \
     check_fvector_size \
     classnametest \
-    conversiontest \
     diagonalmatrixtest \
     dynmatrixtest \
     dynvectortest \

dune/common/test/conversiontest.cc

-// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
-// vi: set et ts=4 sw=2 sts=2:
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
-
-#include <iostream>
-#include <dune/common/typetraits.hh>
-
-int main ()
-{
-  std :: cout << "Conversion from int to double exists? "
-              << Dune::Conversion< int, double > :: exists << std :: endl;
-
-  return 0;
-}

dune/common/typetraits.hh

@@ -131,7 +131,7 @@ namespace Dune
        * @brief True if either a conversion from T1 to T2 or vice versa
        * exists.
        */
-      value = Conversion<T1,T2>::exists || Conversion<T2,T1>::exists
+      value = std::is_convertible<T1,T2>::value || std::is_convertible<T2,T1>::value
     };
   };