Convert a manual query against external accounts into a modern Query

Summary: Depends on D20108. Ref T6703. Update this outdated callsite to a more modern appraoch.

Test Plan: Destroyed a user with `bin/remove destroy`.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T6703

Differential Revision: https://secure.phabricator.com/D20109

src/applications/people/storage/PhabricatorUser.php

@@ -1131,9 +1131,10 @@ final class PhabricatorUser
     $this->openTransaction();
       $this->delete();
 
-      $externals = id(new PhabricatorExternalAccount())->loadAllWhere(
-        'userPHID = %s',
-        $this->getPHID());
+      $externals = id(new PhabricatorExternalAccountQuery())
+        ->setViewer($engine->getViewer())
+        ->withUserPHIDs(array($this->getPHID()))
+        ->execute();
       foreach ($externals as $external) {
         $external->delete();
       }