Make rendered table of contents private in Phriction

Summary: Oops, I missed this -- when properties are `protected`, Lisk assumes they database properties which should be stored and read from the database. To make Lisk ignore a property, make it `private`.

Test Plan:
Should fix this:

{F990757}

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D14538

src/applications/phriction/storage/PhrictionContent.php

@@ -17,11 +17,12 @@ final class PhrictionContent extends PhrictionDAO
   protected $slug;
   protected $content;
   protected $description;
-  protected $renderedTableOfContents;
 
   protected $changeType;
   protected $changeRef;
 
+  private $renderedTableOfContents;
+
   public function renderContent(PhabricatorUser $viewer) {
     return PhabricatorMarkupEngine::renderOneObject(
       $this,