Remove commit from DiffusionRequest

Summary: Ref T2683. This field is //almost// entirely redundant with `symbolicCommit`. Improve how some of the diff query stuff works a bit, then remove it.

Test Plan: Browsed around in all interfaces, looked at a bunch of diffs, etc.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T2683

Differential Revision: https://secure.phabricator.com/D9099

src/applications/diffusion/query/rawdiff/DiffusionMercurialRawDiffQuery.php

@@ -10,7 +10,7 @@ final class DiffusionMercurialRawDiffQuery extends DiffusionRawDiffQuery {
     $drequest = $this->getRequest();
     $repository = $drequest->getRepository();
 
-    $commit = $drequest->getCommit();
+    $commit = $this->getAnchorCommit();
 
     // If there's no path, get the entire raw diff.
     $path = nonempty($drequest->getPath(), '.');