Fix didAbortWorkflow() without workflow

Summary: This is a BC break but it was introduced recently.

Test Plan:
  $ arc unit x

No more:

> Fatal error: Argument 2 passed to ArcanistConfiguration::didAbortWorkflow() must be an instance of ArcanistBaseWorkflow, null given

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3812

src/configuration/ArcanistConfiguration.php

@@ -93,11 +93,7 @@ class ArcanistConfiguration {
     // This is a hook.
   }
 
-  public function didAbortWorkflow(
+  public function didAbortWorkflow($command, $workflow, Exception $ex) {
-    $command,
-    ArcanistBaseWorkflow $workflow,
-    Exception $ex) {
-
     // This is a hook.
   }