ci(docs-infra): do not deploy Firebase Realtime Database rules (#34696)

Currently, the angular.io projects do not use Firebase's Realtime
Database and therefore we only need to configure and deploy changes for
`hosting`.

This commit removes the unused Realtime Database related configs and
files.

PR Close #34696

aio/database.rules.json

@@ -1,6 +0,0 @@
-{
-  "rules": {
-    ".read": "auth != null",
-    ".write": "auth != null"
-  }
-}

aio/firebase.json

@@ -1,7 +1,4 @@
 {
-  "database": {
-    "rules": "database.rules.json"
-  },
   "hosting": {
     "public": "dist",
     "cleanUrls": true,