Remove unnecessary editor styles

These styles were later overwritten by $editorTheme->get_stylesheet()
[MAILPOET-5740]

mailpoet/lib/EmailEditor/Engine/SettingsController.php

@@ -64,7 +64,6 @@ class SettingsController {
     $flexEmailLayoutStyles = file_get_contents(__DIR__ . '/flex-email-layout.css');
 
     $settings['styles'] = [
-      $coreDefaultSettings['defaultEditorStyles'][0],
       ['css' => wp_get_global_stylesheet(['base-layout-styles'])],
       ['css' => $editorTheme->get_stylesheet()],
       ['css' => $contentVariables],