[PL] LIE/HM; Remove unused darcy vel. from IPData.

Alse remove unused computation from computeSecondaryVariableConcreteWithVector().

ProcessLib/LIE/HydroMechanics/LocalAssembler/IntegrationPointDataFracture.h

@@ -50,8 +50,6 @@ struct IntegrationPointDataFracture final
     Eigen::MatrixXd C;
     double integration_weight;
 
-    Eigen::Vector3d darcy_velocity;
-
     void pushBackState()
     {
         w_prev = w;