This is a 'minor' issue as the bug has no effect, but to leave ignored version files if an image was removed by legacy tools; it is listed as 'high' priority, as we want to backport all fixes, minor or not, before the release of 1.4.

It is a regression after
'image-tools: T5831: show system image reverse ordered by date'
which sorts the output of grub.version_list(), but as used in compat.prune_vyos_versions() will have already ignored non-effective version files. The fix is trivial.