Removed use of i18n in Bookshelf plugins

no issue

- i18n is eventually going away in Ghost so we want to remove uses of it
- Bookshelf plugins are also getting extraced out of Ghost so we need to
  remove all local requires
- i18n is being replaced by inline templating with strings stored in the
  `messages` object
- this commit switches out the use of i18n in the Bookshelf plugins and
  replaces the templating function with our `@tryghost/tpl` package

core/server/models/plugins/filter.js

@@ -1,6 +1,10 @@
 const debug = require('ghost-ignition').debug('models:plugins:filter');
-const i18n = require('../../../shared/i18n');
 const errors = require('@tryghost/errors');
+const tpl = require('@tryghost/tpl');
+
+const messages = {
+    errorParsing: 'Error parsing filter'
+};
 
 const RELATIONS = {
     tags: {
@@ -133,8 +137,8 @@ const filter = function filter(Bookshelf) {
                 });
             } catch (err) {
                 throw new errors.BadRequestError({
-                    message: i18n.t('errors.models.plugins.filter.errorParsing'),
+                    message: tpl(messages.errorParsing),
-                    err: err
+                    err
                 });
             }
         }

core/server/models/plugins/pagination.js

@@ -3,8 +3,14 @@
 // Extends Bookshelf.Model with a `fetchPage` method. Handles everything to do with paginated requests.
 const _ = require('lodash');
 
-const i18n = require('../../../shared/i18n');
 const errors = require('@tryghost/errors');
+const tpl = require('@tryghost/tpl');
+
+const messages = {
+    pageNotFound: 'Page not found'
+    couldNotUnderstandRequest: 'Could not understand request.'
+};
+
 let defaults;
 let paginationUtils;
 
@@ -242,7 +248,7 @@ const pagination = function pagination(bookshelf) {
                     .catch(function (err) {
                         // e.g. offset/limit reached max allowed integer value
                         if (err.errno === 20 || err.errno === 1064) {
-                            throw new errors.NotFoundError({message: i18n.t('errors.errors.pageNotFound')});
+                            throw new errors.NotFoundError({message: tpl(messages.pageNotFound)});
                         }
 
                         throw err;
@@ -251,8 +257,8 @@ const pagination = function pagination(bookshelf) {
                 // CASE: SQL syntax is incorrect
                 if (err.errno === 1054 || err.errno === 1) {
                     throw new errors.BadRequestError({
-                        message: i18n.t('errors.models.general.sql'),
+                        message: tpl(messages.couldNotUnderstandRequest),
-                        err: err
+                        err
                     });
                 }