TWANGO1.DEH is NOT REQUIRED. It only contains automap names and intermission text, so it's really just for vanilla players who feel like using it, but again also not required for vanilla either. 

Most modern ports will read the internal DEHACKED lump and/or D/E/Z/MAPINFO, so the standalone file doesn't need to be used at all in that case either.

Does have some funny intermission text though. ;)