Someone is probably on the verge of saying, Why not just leave it in, marked as obsolete? Indeed, according to Webster's, the sense was already long obsolete in 1913:
6. Former; sometime. [Obs.] 'They mourned their ancient leader lost.' Pope.
Okay, fine. If it makes someone happy, go for it, it's not a major deal.
It still seems reasonable to consider, though, whether a sense this, um, ancient is really worth spending time and space on. Which is likely to be greater: the nuisance factor for the 99.99% of users who will have to skim over it, think about it, and mentally discard it, or the undying gratitude of the 0.01% of users who were looking for just that sense and had absolutely no idea from the context?
If LEO were the only hope for that 0.01%, I would say, help the minority by all means. But users seeking specialist historical information can still consult the OED, old dictionaries, or glossed editions of literary texts. Even going by logic and context alone, it's not that great a leap.
In fact, no other modern English dictionary I've checked so far lists the sense, even marked as obsolete.
And maybe it's just me, but I don't notice anything like as determined a push to add or defend entries for German words now found only in, say, Grimm or Adelung. Why is that? Are so many LEO users devoted fans of Alexander Pope, and none of Bach or Goethe? Please, O ye capricious literary gods, say it isn't so... (-;