notif: remove code migrated to tcef-notifications microservice

The push/email notification processing now lives in the tcef-notifications
service (fases 1a-1c). Removed from the web:
- imports/startup/server/notificationsObserver.js (observe Notifications -> processNotif)
- imports/modules/server/notificationsProcess.js (node-gcm push + notif emails)
- the 'Process pending notif' SyncedCron job in cron.js
- node-gcm dependency (dead Google API since jun-2024)

subsUnion.js is KEPT: it feeds the subs-public-union SiteSettings that the REST
API (status/subs-public-union) serves to the Flutter app; it is not part of the
notifications pipeline.

DEPLOY ORDERING (see UPGRADE.md): production must not run this build until the
tcef-notifications service is emitting in prod — otherwise notifications stop.
REST smoke test green (byte-identical).

imports/startup/server/index.js

@@ -8,7 +8,6 @@ import './fixtures';
 import './email';
 import './IPGeocoder';
 import './migrations';
-import './notificationsObserver';
 import './facts';
 import './comments';
 import './sitemaps';