remove mail fake failures method (#44003)

Author: crissi

src/Illuminate/Support/Testing/Fakes/MailFake.php

@@ -393,16 +393,6 @@ public function later($delay, $view, $queue = null)
         $this->queue($view, $queue);
     }
 
-    /**
-     * Get the array of failed recipients.
-     *
-     * @return array
-     */
-    public function failures()
-    {
-        return [];
-    }
-
     /**
      * Infer mailable class using reflection if a typehinted closure is passed to assertion.
      *