Drop volumes key from manifest

maubot-src/CloudronManifest.json

@@ -29,11 +29,5 @@
     "maubot"
   ],
   "postInstallMessage": "The Maubot UI is protected by Cloudron SSO. The initial API/UI admin credentials are stored in /app/data/.admin_password (username: root). Retrieve them with `cloudron exec --app <app-id> -- cat /app/data/.admin_password` before first login.",
-  "volumes": [
-    {
-      "name": "data",
-      "path": "/app/data"
-    }
-  ],
   "displayName": "Maubot"
 }