Removed unsed method GetStress and PlotFibres (now: PlotFibreOrientation)

src/elasticity/assemble/DGElasticity.cpp

src/elasticity/assemble/DGElasticity.hpp

src/elasticity/assemble/EGElasticity.cpp

src/elasticity/assemble/EGElasticity.hpp

src/elasticity/assemble/LagrangeElasticity.cpp

src/elasticity/assemble/LagrangeElasticity.hpp