[HT] Removed an unused member, fluid_reference_density

Documentation/ProjectFile/prj/processes/process/HT/t_fluid_reference_density.md

-Reference value of the fluid density used in the equation of state for the fluid
-density as well as in the calculation of the thermal dispersivity and head
-capacity.

ProcessLib/HT/CreateHTProcess.cpp

@@ -58,14 +58,6 @@ std::unique_ptr<Process> createHTProcess(
     auto fluid_properties =
         MaterialLib::Fluid::createFluidProperties(fluid_config);
 
-    // Parameter for the density of the fluid.
-    auto& fluid_reference_density = findParameter<double>(
-        config,
-        //! \ogs_file_param_special{prj__processes__process__HT__fluid_reference_density}
-        "fluid_reference_density", parameters, 1);
-    DBUG("Use \'%s\' as fluid_reference_density parameter.",
-         fluid_reference_density.name.c_str());
-
     // Parameter for the density of the solid.
     auto& density_solid = findParameter<double>(
         config,
@@ -179,7 +171,6 @@ std::unique_ptr<Process> createHTProcess(
         std::make_unique<HTMaterialProperties>(
             std::move(porous_media_properties),
             density_solid,
-            fluid_reference_density,
             std::move(fluid_properties),
             *thermal_dispersivity_longitudinal,
             *thermal_dispersivity_transversal,

ProcessLib/HT/HTMaterialProperties.h

@@ -28,7 +28,6 @@ struct HTMaterialProperties
         MaterialLib::PorousMedium::PorousMediaProperties&&
             porous_media_properties_,
         ProcessLib::Parameter<double> const& density_solid_,
-        ProcessLib::Parameter<double> const& fluid_reference_density_,
         std::unique_ptr<MaterialLib::Fluid::FluidProperties>&&
             fluid_properties_,
         ProcessLib::Parameter<double> const& thermal_dispersivity_longitudinal_,
@@ -42,7 +41,6 @@ struct HTMaterialProperties
         bool const has_gravity_)
         : porous_media_properties(std::move(porous_media_properties_)),
           density_solid(density_solid_),
-          fluid_reference_density(fluid_reference_density_),
           fluid_properties(std::move(fluid_properties_)),
           specific_heat_capacity_solid(specific_heat_capacity_solid_),
           thermal_dispersivity_longitudinal(thermal_dispersivity_longitudinal_),
@@ -58,7 +56,6 @@ struct HTMaterialProperties
 
     MaterialLib::PorousMedium::PorousMediaProperties porous_media_properties;
     Parameter<double> const& density_solid;
-    Parameter<double> const& fluid_reference_density;
     std::unique_ptr<MaterialLib::Fluid::FluidProperties> fluid_properties;
     Parameter<double> const& specific_heat_capacity_solid;
     Parameter<double> const& thermal_dispersivity_longitudinal;