[T/HT] Rm porous_medium tag from project files.

Tests/Data/Parabolic/HT/ConstViscosity/square_5500x5500.prj

...nthetics/CoupledPressureParabolicTemperatureParabolic.prj

...CoupledPressureParabolicTemperatureParabolicStaggered.prj

...ata/Parabolic/HT/SimpleSynthetics/IsothermalFluidFlow.prj

...olic/HT/SimpleSynthetics/IsothermalFluidFlowStaggered.prj

...ic/HT/SimpleSynthetics/IsothermalFluidFlowWithGravity.prj

...pleSynthetics/IsothermalFluidFlowWithGravityStaggered.prj

...impleSynthetics/PressureDiffusionTemperatureDiffusion.prj

...hetics/PressureDiffusionTemperatureDiffusionStaggered.prj

...impleSynthetics/PressureParabolicTemperatureParabolic.prj

...hetics/PressureParabolicTemperatureParabolicStaggered.prj

.../HT/SimpleSynthetics/calculatesurfaceflux_ht_cube_1e3.prj

.../HT/SimpleSynthetics/calculatesurfaceflux_ht_cube_1e4.prj

.../Data/Parabolic/HT/SimpleSynthetics/constraint_bc_1e3.prj

...redCoupling/ADecovalexTHMCBasedHTExample/th_decovalex.prj

...ling/ConstViscosity/square_5500x5500_staggered_scheme.prj

...scosity/square_5500x5500_staggered_scheme_adaptive_dt.prj