Remove unused dependencies from I18n and newsletter editor scripts

assets/js/src/i18n.js

@@ -1,10 +1,8 @@
 define('i18n',
   [
-    'mailpoet',
-    'underscore',
+    'mailpoet'
   ], function(
-    MailPoet,
-    _
+    MailPoet
 ) {
   'use strict';
 

assets/js/src/newsletter_editor/App.js

@@ -1,12 +1,11 @@
 define([
     'backbone',
     'backbone.marionette',
-    'backbone.supermodel',
     'jquery',
     'underscore',
     'handlebars',
     'handlebars_helpers'
-  ], function(Backbone, Marionette, SuperModel, jQuery, _, Handlebars) {
+  ], function(Backbone, Marionette, jQuery, _, Handlebars) {
 
   var app = new Marionette.Application(), AppView;