pilon 1.22+dfsg-2~bpo9+2 fixes this issue.
- Bug#911513: pilon: uninstallable in stretch-bac... Andreas Beckmann
- Bug#911513: pilon: uninstallable in stretc... Andreas Tille
- Bug#911513: marked as done (pilon: uninsta... Debian Bug Tracking System
pilon 1.22+dfsg-2~bpo9+2 fixes this issue.