Moving fetching iframed assets

Because we called the function for getting editor iframed assets in init hook, it could cause that some properties were not set yet.

packages/php/email-editor/tests/integration/_bootstrap.php

@@ -321,7 +321,6 @@ abstract class MailPoetTest extends \Codeception\TestCase\Test { // phpcs:ignore
 					$container->get( Email_Api_Controller::class ),
 					$container->get( Templates::class ),
 					$container->get( Patterns::class ),
-					$container->get( Settings_Controller::class ),
 					$container->get( Send_Preview_Email::class ),
 					$container->get( Personalization_Tags_Registry::class ),
 				);