[MatL] Remove unused getGasDensityDerivative().

TwoPhaseFlowWithPPMaterialProperties::getGasDensityDerivative

MaterialLib/TwoPhaseModels/TwoPhaseFlowWithPPMaterialProperties.cpp

@@ -90,16 +90,6 @@ double TwoPhaseFlowWithPPMaterialProperties::getGasDensity(const double p,
     return _gas_density->getValue(vars);
 }
 
-double TwoPhaseFlowWithPPMaterialProperties::getGasDensityDerivative(
-    const double p, const double T) const
-{
-    ArrayType vars;
-    vars[static_cast<int>(MaterialLib::Fluid::PropertyVariableType::T)] = T;
-    vars[static_cast<int>(MaterialLib::Fluid::PropertyVariableType::p)] = p;
-
-    return _gas_density->getdValue(vars,
-                                   MaterialLib::Fluid::PropertyVariableType::p);
-}
 double TwoPhaseFlowWithPPMaterialProperties::getLiquidViscosity(
     const double p, const double T) const
 {

MaterialLib/TwoPhaseModels/TwoPhaseFlowWithPPMaterialProperties.h

@@ -98,7 +98,6 @@ public:
     double getGasDensity(const double p, const double T) const;
     double getGasViscosity(const double p, const double T) const;
     double getLiquidViscosity(const double p, const double T) const;
-    double getGasDensityDerivative(double const p, double const T) const;
     double getNonwetRelativePermeability(
         const double t, const ParameterLib::SpatialPosition& pos,
         const double p, const double T, const double saturation) const;