Kill CD support

src/Makefile

src/Makefile.cfg

src/d_main.c

src/d_netcmd.c

src/i_sound.h

src/p_setup.c

src/s_sound.c

src/s_sound.h

src/sdl/CMakeLists.txt

src/sdl/i_cdmus.c

src/sdl/i_system.c