Don't write inverse edges for DifferentialRevisionHasReviewerEdgeType

Summary: The default behavior was inadvertedly changed in D11074. This restores the original behavior.

Test Plan: Added a project reviewer to a diff, saw no inverse transaction recorded.

Reviewers: Krenair, epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11181

src/applications/differential/edge/DifferentialRevisionHasReviewerEdgeType.php

@@ -9,10 +9,6 @@ final class DifferentialRevisionHasReviewerEdgeType
     return DifferentialReviewerForRevisionEdgeType::EDGECONST;
   }
 
-  public function shouldWriteInverseTransactions() {
-    return true;
-  }
-
   public function getTransactionAddString(
     $actor,
     $add_count,