Change piggy_register_sound to take the sound offset as a parameter,
rather than assuming the caller will set SoundOffset accordingly.
Remove a spurious sound reset in piggy_register_bitmap. Based on the
duplicated comment, this was probably incorrectly copied from
piggy_register_sound, where it made sense, into piggy_register_bitmap,
where it does not.
gamedata_read_tbl is only called if (D1 || (D2 && EDITOR)). Exclude
defining it for (D2 && !EDITOR). From there, also exclude defining or
reading the alias list, which is only written by a function
called by gamedata_read_tbl.
Reported-by: heftig <https://github.com/dxx-rebirth/dxx-rebirth/issues/642>