Fixed "Route#router intimate API" deprecation notices

closes https://github.com/TryGhost/Ghost/issues/9603
- don't add a `setTitle` method on the router and instead call `window.document.title` directly so that we don't have to access  `Route#router` (throws deprecation) or `Route#_router` (private and may break without notice)

ghost/admin/app/routes/application.js

@@ -35,12 +35,10 @@ export default Route.extend(ApplicationRouteMixin, ShortcutsRoute, {
     feature: service(),
     ghostPaths: service(),
     notifications: service(),
+    router: service(),
     settings: service(),
     tour: service(),
     ui: service(),
-    // TODO: rename to `router` when we drop using of Route#router in our
-    // document-title util
-    routerService: service('router'),
 
     shortcuts,
 
@@ -197,7 +195,7 @@ export default Route.extend(ApplicationRouteMixin, ShortcutsRoute, {
                 }
 
                 let routeInfo = transition.handlerInfos[transition.handlerInfos.length - 1];
-                let router = this.get('routerService');
+                let router = this.get('router');
                 let params = [];
 
                 for (let key of Object.keys(routeInfo.params)) {

ghost/admin/app/utils/document-title.js

@@ -39,7 +39,7 @@ export default function () {
                         finalTitle = this.title;
                     }
 
-                    this.router.setTitle(finalTitle);
+                    window.document.title = finalTitle;
                 } else {
                     return true;
                 }
@@ -50,10 +50,6 @@ export default function () {
     Router.reopen({
         updateTitle: on('didTransition', function () {
             this.send('collectTitleTokens', []);
-        }),
-
-        setTitle(title) {
-            window.document.title = title;
-        }
+        })
     });
 }