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).

package.json

@@ -49,7 +49,6 @@
     "modernizr": "^3.6.0",
     "moment": "^2.19.1",
     "moment-timezone": "^0.5.14",
-    "node-gcm": "^1.0.2",
     "node-geocoder": "^3.21.1",
     "node-gyp": "^3.7.0",
     "nodemailer": "^4.4.2",