[TM] Removed ThermoMechanicsProcessData::reference_temperature

...esses/process/THERMO_MECHANICS/t_reference_temperature.md

ProcessLib/ThermoMechanics/CreateThermoMechanicsProcess.cpp

ProcessLib/ThermoMechanics/ThermoMechanicsProcessData.h

...pBGRa/SimpleAxisymmetricCreep/SimpleAxisymmetricCreep.prj

...tricCreep/SimpleAxisymmetricCreepWithAnalyticSolution.prj

Tests/Data/ThermoMechanics/cube_1e3.prj

...s/Data/ThermoMechanics/iglu_axisymmetric_plane_strain.prj

...a/ThermoMechanics/iglu_axisymmetric_plane_strain_quad.prj

Tests/Data/ThermoMechanics/iglu_quarter_plane_strain.prj

...s/Data/ThermoMechanics/iglu_quarter_plane_strain_quad.prj