Added billing controller for explicitness

refs d691b15

- Additionally removed redundant super call

ghost/admin/app/controllers/billing.js

@@ -0,0 +1,9 @@
+import Controller from '@ember/controller';
+import {alias} from '@ember/object/computed';
+
+export default Controller.extend({
+    queryParams: ['action'],
+    action: null,
+
+    guid: alias('model')
+});

ghost/admin/app/routes/billing.js

@@ -8,10 +8,6 @@ export default Route.extend({
         action: {refreshModel: true}
     },
 
-    init() {
-        this._super(...arguments);
-    },
-
     model(params) {
         if (params.action) {
             this.billing.set('action', params.action);