Stray TODO comment in colorsys.pyi

[Andrew5057]

After seeing the # TODO comment in colorsys.pyi (line 12) noting that ONE_SIXTH et al. are undocumented, I opened a CPython issue to document them, which was closed (for good reason) as not planned. Given that, what should we do about the comment? Imo, either removing it entirely or linking to that PR would be okay.

[srittau]

This comment has been virtually unchanged since the before times (i.e. 2016). Our usual policy is to mark undocumented items with an # undocumented comment (or more often than not not mark it at all). No need to link any issues. So we should just remove the TODO: marker.