Use EditDistanceMatrix diff smoothing in Arcanist
Since it now is, call it instead of keeping a copy of the logic around.
Previously, the unit tests were testing un-smoothed diffs. Just have them test smoothed diffs instead, since nothing actually uses unsmoothed diffs.
Test Plan: Pasted a raw diff into the web UI, got a sensible inline diff for it.
Reviewed By: chad
Maniphest Tasks: T7643
Differential Revision: https://secure.phabricator.com/D16069