Revert "Switch to std::uint_least32_t for stored indices in MatrixIndexSet"

This reverts commit 4886d18b.

dune/istl/matrixindexset.hh

@@ -31,7 +31,7 @@ namespace Dune {
    */
   class MatrixIndexSet
   {
-    using Index = std::uint_least32_t;
+    using Index = std::size_t;
 
     // A vector that partly mimics a std::set by staying
     // sorted on insert() and having unique values.

dune/python/istl/matrixindexset.hh

@@ -3,7 +3,6 @@
 #ifndef DUNE_PYTHON_ISTL_BCRSMATRIX_HH
 #define DUNE_PYTHON_ISTL_BCRSMATRIX_HH
 
-#include <cstdint>
 #include <memory>
 #include <stdexcept>
 #include <string>
@@ -30,7 +29,7 @@ namespace Dune
     void registerMatrixIndexSet(pybind11::handle scope,
                             pybind11::class_<MatrixIndexSet, options...> cls)
     {
-      using size_type = Dune::MatrixIndexSet::size_type;
+      typedef std::size_t size_type;
 
       // two different possible constructors
       cls.def( pybind11::init( [] () { return new MatrixIndexSet(); } ) );