Expose mixin for inheritance, fix some spacing.

Related to https://github.com/OCA/web/pull/481.

web_x2many_delete_all/static/src/js/web_x2many_delete_all.js

@@ -1,10 +1,9 @@
 /* Copyright 2016 Onestein
  * License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). */
 
-odoo.define('web_x2many_delete_all', function (require) {
+odoo.define('web_x2many_delete_all.Mixin', function (require) {
     "use strict";
-    var core = require('web.core'),
-        _t = core._t;
+    var core = require('web.core');
 
     var X2ManyListDeleteAllMixin = {
         events: {
@@ -36,4 +35,6 @@ odoo.define('web_x2many_delete_all', function (require) {
 
     core.form_widget_registry.get('many2many').include(X2ManyListDeleteAllMixin);
     core.form_widget_registry.get('one2many').include(X2ManyListDeleteAllMixin);
+
+    return X2ManyListDeleteAllMixin;
 });