remove unused use statement

Author: saeideng

config/app.php

@@ -3,7 +3,6 @@
 use Cake\Cache\Engine\FileEngine;
 use Cake\Database\Connection;
 use Cake\Database\Driver\Mysql;
-use Cake\Error\ExceptionRenderer;
 use Cake\Log\Engine\FileLog;
 use Cake\Mailer\Transport\MailTransport;