Remove duplicate loop

Shame on me for introducing this! Surprisingly no one ever
bothered to setup the whole matrix hierarchy twice.

Thanks to Elias for pointing me to this.

[[Imported from SVN: r4978]]

dune/solvers/iterationsteps/multigridstep.cc

@@ -99,9 +99,6 @@ void MultigridStep<MatrixType, VectorType, BitVectorType>::preprocess()
     } else 
         DUNE_THROW(SolverError, "We need a set of nodes to ignore");
 
-    for (i=this->mgTransfer_.size()-1; i>=0; i--) 
-        this->mgTransfer_[i]->galerkinRestrict(*this->mat_[i+1], *(const_cast<MatrixType*>(this->mat_[i])));
-
     // /////////////////////////////////////////////
     //   Set up base solver
     // /////////////////////////////////////////////