[Cleanup] Kill an assertion (the code was buggy, too)

dune/tectonic/myblockproblem.hh

@@ -170,26 +170,6 @@ template <class MyConvexProblemTypeTEMPLATE> class MyBlockProblem {
     // -grad is needed for Newton step
     linearization.b *= -1.0;
 
-    // b should be a descent direction
-    {
-      VectorType const direction = linearization.b;
-      VectorType tmp = linearization.b;                      //  b
-      Arithmetic::addProduct(tmp, -1.0, linearization.A, u); // b-Au
-      double const localA = tmp * direction;                 // <b-Au,v>
-
-      linearization.A.mv(direction, tmp);    //  Av
-      double const localb = tmp * direction; // <Av,v>
-
-      MyDirectionalConvexFunction<
-          Dune::GlobalNonlinearity<MatrixType, VectorType>> const
-      psi(localA, localb, problem.phi, u, direction);
-
-      Interval<double> D;
-      psi.subDiff(0, D);
-      if (!isnan(D[1]))
-        assert(D[1] <= 0);
-    }
-
     // apply truncation to stiffness matrix and rhs
     for (size_t row = 0; row < linearization.A.N(); ++row) {
       auto const col_end = linearization.A[row].end();