The Bird type is the only intentionally created type to have been scrapped entirely from the games. The discontinued types, like Shadow and ???, do not count, as they have been in games before being removed.
If we want to talk about unintentional types that didn't make the cut, however, there's quite a few more. To quote Bulbapedia:
The glitch types are types which only appear through the use of glitches, such as on the types of glitch Pokémon. Most famously this includes the Bird type, which was intentionally programmed into the code of the Generation I and II games but was not given to any real Pokémon. Other glitch types are the result of the game reading other data as if it were types. Like the ??? type, all glitch types, except 'l) m) ZM, have no special effectiveness (they both inflict regular damage against all types and take regular damage from all types).
There's a lot of glitch types, and these two links list them all.
Generation I Glitch Types
Generation II Glitch Types
