Removed support of old Ascii scenery format. The loader had not been

Removed support of old Ascii scenery format.  The loader had not been
maintianed or upgraded in a *long* time so it didn't support many new
features like the runway lighting.  If anyone was using it for anything,
it should not be a huge amount of work to switch to the binary format.
SimGear includes a reader and writer for the binary format.