remove no longer used service definition

Author: xabbuh

Resources/config/mailer.php

@@ -45,7 +45,6 @@
                 tagged_iterator('mailer.transport_factory'),
             ])
 
-        ->set('mailer.default_transport', TransportInterface::class)
         ->alias('mailer.default_transport', 'mailer.transports')
         ->alias(TransportInterface::class, 'mailer.default_transport')