Fix arc unit --everything

Summary: This was broken in D13573.

Test Plan: Ran `arc unit --everything` in rPHU.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D13864

src/unit/engine/PhutilUnitTestEngine.php

@@ -80,9 +80,11 @@ final class PhutilUnitTestEngine extends ArcanistUnitTestEngine {
   private function getAllTests() {
     $project_root = $this->getWorkingCopy()->getProjectRoot();
 
-    $symbols = id(new PhutilClassMapQuery())
+    $symbols = id(new PhutilSymbolLoader())
+      ->setType('class')
       ->setAncestorClass('PhutilTestCase')
-      ->execute();
+      ->setConcreteOnly(true)
+      ->selectSymbolsWithoutLoading();
 
     $in_working_copy = array();