VTKBasisGridFunction: do not check size in constructor

With a Dune::VTKSequenceWriter I would like to have code like

    Vector x;
    VTKSequenceWriter<...> writer(...);
    VTKBasisGridFunction<...> function(..., x, ...);
    writer.addVertexData(function);

    for (int i = 0; i < level; ++i) {
        ... // refine grid, solve PDE, change size of x
        writer.write(static_cast<double>(i));
    }

As the size of "x" is only correct in the for-loop, it cannot be checked
when constructing the "writer". However the "function" needs to be setup
outside the loop as well. So the VTKBasisGridFunction constructor should
not check the size of "x".

dune/fufem/functions/vtkbasisgridfunction.hh

@@ -34,8 +34,7 @@ public:
         coeffs_(v),
         s_( s )
     {
-        if (v.size() !=basis_.size())
-            DUNE_THROW(Dune::IOError, "VTKGridFunction: Coefficient vector is not matching the basis");
+        /* Nothing. */
     }
 
     /** \brief Get the number of components the function has. */