12 years ago, old_des.h was used to provide compatibility with libdes.

12 years ago, old_des.h was used to provide compatibility with libdes.
The man page says "Compatibility des_ functions are provided for a short
while" and indeed even the original commit message says "The compatibility
functions will be removed in some future release, at the latest in
version 1.0." So here we are, a short while later.

Now I've only been an OpenBSD developer for 11 years, one year less than
this header has existed, but in that brief time, I've learned a thing or
two about deleting obsolete code. It doesn't delete itself. And worse,
people will continue using it until you force them onto a better path.