zico removed all uses of these classes in 3366658a5b, but did not
remove their definitions. No one has tried to repurpose them, so remove
the definitions.
Fixes: 3366658a5b ("Updated 'Netgame Rules & Info' screen, added option to toggle it ingame via SHIFT-PAUSE, added hint to netgame help menu")
Descent 1 has no headlight powerup. Code to read headlights was
incorrectly added in 357e1b0144, but no code was added to write
headlights, so the Descent 1 lighting code checked for headlights that
never existed. Guard the headlight global variables and the associated
logic with if(D2).
Fixes: 357e1b0144 ("Made lighting code work with actual RGB values and added feature to let certain objects emit colored dynamic light as well as let mine flash red when control center destroyed (OpenGL-only at the moment)")
Type `SyncGLMethod` was defined conditional on DXX_USE_OGL, but header
`common/include/ogl_sync.h` used `SyncGLMethod` unconditionally. This
works fine in the normal build since SDL builds never include
`common/include/ogl_sync.h`, but broke the check_header_includes=1 test
since that compiles `common/include/ogl_sync.h` even for SDL builds.
Wrap type `ogl_sync` in `#if DXX_USE_OGL` to hide it from the
check_header_includes=1 test in SDL mode.