[cleanup][cartesian] restore factor 2 for cartesian grids.

dune/fem-dg/operator/limiter/limiterutility.hh

@@ -407,8 +407,7 @@ namespace Fem
           point -= entityCenter;
 
           const double length = (point * lambda);
-          //const double factorLength = (cartesianGrid) ? 2.0 * length : length ;
-          const double factorLength = length;//(cartesianGrid) ? 2.0 * length : length ;
+          const double factorLength = (cartesianGrid) ? 2.0 * length : length ;
           lambda *= factorLength;
 
           assert( lambda.two_norm () > 0 );