Allow file comments to be edited

Summary:
Fixes T10750. Files have some outdated cache/key code which prevents recording an edit history on file comments.

Remove this ancient cruft.

(Users must `bin/storage adjust` after upgrading to this patch to reap the benefits.)

Test Plan:
  - Ran `bin/storage adjust`.
  - Edited a comment in Files.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10750

Differential Revision: https://secure.phabricator.com/D16312

src/applications/files/storage/PhabricatorFileTransactionComment.php

@@ -7,20 +7,4 @@ final class PhabricatorFileTransactionComment
     return new PhabricatorFileTransaction();
   }
 
-  public function shouldUseMarkupCache($field) {
-    // Only cache submitted comments.
-    return ($this->getTransactionPHID() != null);
-  }
-
-  protected function getConfiguration() {
-    $config = parent::getConfiguration();
-    $config[self::CONFIG_KEY_SCHEMA] = array(
-      'key_draft' => array(
-        'columns' => array('authorPHID', 'transactionPHID'),
-        'unique' => true,
-      ),
-    ) + $config[self::CONFIG_KEY_SCHEMA];
-    return $config;
-  }
-
 }