"telnetlib" Python module removed in 3.13

[olebole]

In the upcoming Python 3.13 version, the original "telnetlib" Python modules is removed. This modules is used in

astrometry.net/util/horizons.py

Line 11 in fb1342a

import telnetlib as tn

This was reported as Debian#1084555.

[dstndstn]

hmm, the horizons.py script isn't actually used by anything else, it was something we developed for other projects and just dumped it in the Astrometry.net repo because it's generally related to doing astrometry work. (Horizons is JPL's service for ephemerides.)