Core API simplification: remove c'tors XSimulation(sample)

Core/Simulation/DepthProbeSimulation.cpp

Core/Simulation/DepthProbeSimulation.h

Core/Simulation/GISASSimulation.cpp

Core/Simulation/GISASSimulation.h

Core/Simulation/OffSpecSimulation.cpp

Core/Simulation/OffSpecSimulation.h

Core/Simulation/Simulation.cpp

Core/Simulation/Simulation.h

Core/Simulation/Simulation2D.cpp

Core/Simulation/Simulation2D.h

Core/Simulation/SpecularSimulation.cpp

Core/Simulation/SpecularSimulation.h

GUI/coregui/Models/DomainSimulationBuilder.cpp

Tests/Functional/Python/PyFit/fitobjective_api.py

Tests/UnitTests/Core/Fitting/FittingTestHelper.h

Tests/UnitTests/Core/Other/GISASSimulationTest.cpp

auto/Wrap/libBornAgainCore.py

auto/Wrap/libBornAgainCore_wrap.cpp