Removed no longer needed hack

The hack done here: https://github.com/meteor/meteor/blob/devel/packages/less/plugin/compile-less.js#L47
 now backfires on my system and is reporting a line number one less than the actual error. I don't know when this behaviour has changed, but I have tested this in multiple scenarios.

(I also see that the less library package is a bit outdated.)
Is the ` +1` still needed?

cc @christianbundy for https://github.com/mquandalle/meteor-harmony/commit/f79a3f0338a2184f613dcc9ccdc67f15449c1c7d