Remove obsolete code and adjust tests

Core/Computation/ConstantBackground.cpp

Core/Computation/IBackground.cpp

Core/Computation/IBackground.h

Core/Computation/PoissonNoiseBackground.cpp

Core/Computation/SpecularComputation.cpp

Core/Computation/SpecularComputationTerm.cpp

Core/Computation/SpecularComputationTerm.h

Core/Instrument/SpecularDetector1D.cpp

Core/Instrument/SpecularDetector1D.h

Core/Multilayer/IFresnelMap.h

Core/Multilayer/MatrixFresnelMap.cpp

Core/Multilayer/MatrixFresnelMap.h

Core/Multilayer/ScalarFresnelMap.cpp

Core/Multilayer/ScalarFresnelMap.h

Core/Simulation/SpecularSimulation.cpp

Tests/UnitTests/Core/Detector/SpecularDetector1DTest.h