Remove remnants of OS/2 support, which has been broken at least since
commit 9831fa553c from 2006-10, but more probably even since after
gphoto2 2.1.0 which was some time in 2002.
Closes: https://github.com/gphoto/libgphoto2/issues/710
Rules for the API docs:
1. DO NOT DOCUMENT ANYTHING YET
2. If you know a method to keep API docs and internal docs apart, with
doxygen, please tell us.
3. If this has been solved, start documenting the external interface.
Thank you.