[HM] remove Kpu_k

ProcessLib/HydroMechanics/HydroMechanicsFEM-impl.h

@@ -335,7 +335,6 @@ void HydroMechanicsLocalAssembler<ShapeFunctionDisplacement,
         if constexpr (pressure_size == displacement_size)
         {
             Kpu = Kpu.colwise().sum().eval().asDiagonal();
-            Kpu_k = Kpu_k.colwise().sum().eval().asDiagonal();
         }
     }