remove the backup check notification and route

it seems we decided that instead of a notification, we display a warning in
the backups view itself (see #719).

src/server.js

@@ -140,7 +140,6 @@ function initializeExpressSync() {
     router.get ('/api/v1/backups',               token, authorizeAdmin, routes.backups.list);
     router.post('/api/v1/backups/create',        token, authorizeAdmin, routes.backups.startBackup);
     router.post('/api/v1/backups/cleanup', json, token, authorizeAdmin, routes.backups.cleanup);
-    router.get ('/api/v1/backups/check',         token, authorizeAdmin, routes.backups.check);
 
     // config route (for dashboard). can return some private configuration unlike status
     router.get ('/api/v1/config', token, routes.cloudron.getConfig);