Remove i18n dependency from notifications service

refs https://github.com/TryGhost/Ghost/issues/13380

- The i18n package is deprecated. It is being replaced with the tpl package.

core/server/services/notifications/index.js

@@ -1,12 +1,10 @@
 const settingsCache = require('../../../shared/settings-cache');
-const i18n = require('../../../shared/i18n');
 const ghostVersion = require('@tryghost/version');
 const Notifications = require('./notifications');
 const models = require('../../models');
 
 module.exports.notifications = new Notifications({
     settingsCache,
-    i18n,
     ghostVersion,
     SettingsModel: models.Settings
 });

core/server/services/notifications/notifications.js

@@ -3,21 +3,25 @@ const semver = require('semver');
 const Promise = require('bluebird');
 const _ = require('lodash');
 const errors = require('@tryghost/errors');
+const tpl = require('@tryghost/tpl');
 const ObjectId = require('bson-objectid');
 
+const messages = {
+    noPermissionToDismissNotif: 'You do not have permission to dismiss this notification.',
+    notificationDoesNotExist: 'Notification does not exist.'
+};
+
 class Notifications {
     /**
      *
      * @param {Object} options
      * @param {Object} options.settingsCache - settings cache instance
-     * @param {Object} options.i18n - i18n instance
      * @param {Object} options.ghostVersion
      * @param {String} options.ghostVersion.full - Ghost instance version in "full" format - major.minor.patch
      * @param {Object} options.SettingsModel - Ghost's Setting model instance
      */
-    constructor({settingsCache, i18n, ghostVersion, SettingsModel}) {
+    constructor({settingsCache, ghostVersion, SettingsModel}) {
         this.settingsCache = settingsCache;
-        this.i18n = i18n;
         this.ghostVersion = ghostVersion;
         this.SettingsModel = SettingsModel;
     }
@@ -195,13 +199,13 @@ class Notifications {
 
         if (notificationToMarkAsSeenIndex > -1 && !notificationToMarkAsSeen.dismissible) {
             return Promise.reject(new errors.NoPermissionError({
-                message: this.i18n.t('errors.api.notifications.noPermissionToDismissNotif')
+                message: tpl(messages.noPermissionToDismissNotif)
             }));
         }
 
         if (notificationToMarkAsSeenIndex < 0) {
             return Promise.reject(new errors.NotFoundError({
-                message: this.i18n.t('errors.api.notifications.notificationDoesNotExist')
+                message: tpl(messages.notificationDoesNotExist)
             }));
         }