eclipse: remove old to-do comment about "mirror://eclipse/"

The comment is from 2011, before we started using officially mirrored
URLs[1] like

  http://www.eclipse.org/downloads/download.php?r=1&nf=1&file=THE_FILE

I think using upstream mirrored URLs is better than mirror://eclipse:

  - upstream mirror list is always up to date
  - the closest / fastest mirror will be selected automatically

[1]: http://wiki.eclipse.org/IT_Infrastructure_Doc#Use_mirror_sites.2Fsee_which_mirrors_are_mirroring_my_files.3F