Only expose log in post-step hook

The log has step ID and workflow run ID in case an integration needs to
retrieve them.

[MAILPOET-4463]

mailpoet/lib/Automation/Engine/Control/StepHandler.php

@@ -130,7 +130,7 @@ class StepHandler {
         throw $e;
       } finally {
         try {
-          $this->hooks->doWorkflowStepAfterRun($step, $log);
+          $this->hooks->doWorkflowStepAfterRun($log);
         } catch (Exception $e) {
           $log->addError($e);
         }