Mark person that actually runs arc commit as committer instead of the author.

Summary:
`arc commit` and `arc mark-committed` would only add comments <author> committed
this revision, since now everyone can run this commands it makes more sense to
show the actual committer instead of the author.

Test Plan:
Commit (or mark committed) not your revision, Phabricator should add <you>
committed this revision comment instead of <author> committed this revision.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: 1067

src/applications/conduit/method/differential/markcommitted/ConduitAPI_differential_markcommitted_Method.php

@@ -62,7 +62,7 @@ class ConduitAPI_differential_markcommitted_Method extends ConduitAPIMethod {
 
     $editor = new DifferentialCommentEditor(
       $revision,
-      $revision->getAuthorPHID(),
+      $request->getUser()->getPHID(),
       DifferentialAction::ACTION_COMMIT);
     $editor->save();
 

src/applications/differential/editor/comment/DifferentialCommentEditor.php

@@ -240,9 +240,6 @@ class DifferentialCommentEditor {
         break;
 
       case DifferentialAction::ACTION_COMMIT:
-        if (!$actor_is_author) {
-          throw new Exception('You can not commit a revision you do not own.');
-        }
         $revision
           ->setStatus(DifferentialRevisionStatus::COMMITTED)
           ->save();