Remove demos and missing contrib/bessel

contrib/bessel/Bessel.cpp

contrib/bessel/Bessel.h

contrib/bessel/BesselLib.f

contrib/bessel/CMakeLists.txt

examples/helmholtzFlow/Duct_ABCs/CMakeLists.txt

examples/helmholtzFlow/Duct_ABCs/main.cpp

examples/helmholtzFlow/Duct_PMLs/CMakeLists.txt

examples/helmholtzFlow/Duct_PMLs/main.cpp

examples/helmholtzFlow/FreeField/CMakeLists.txt

examples/helmholtzFlow/FreeField/main.cpp

examples/helmholtzFlow/helmholtzDuctHeteroX/CMakeLists.txt

examples/helmholtzFlow/helmholtzDuctHeteroX/main.cpp

...s/helmholtzFlow/helmholtzDuctHeteroX/main_loop_length.cpp

...es/helmholtzFlow/helmholtzDuctHeteroX/main_loop_omega.cpp

examples/helmholtzFlow/helmholtzDuctHeteroY/CMakeLists.txt

examples/helmholtzFlow/helmholtzDuctHeteroY/main.cpp

...s/helmholtzFlow/helmholtzDuctHeteroY/main_loop_length.cpp

...es/helmholtzFlow/helmholtzDuctHeteroY/main_loop_omega.cpp

...ples/helmholtzFlow/helmholtzflow/Duct_ABCs/main_omega.cpp

...s/helmholtzFlow/helmholtzflow/Duct_HeteroX/CMakeLists.txt