Delete nextcloud-exporter (addon) after migration to ProxmoxVE (#1235)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

frontend/public/json/nextcloud-exporter.json

@@ -1,35 +0,0 @@
-{
-  "name": "Nextcloud Exporter",
-  "slug": "nextcloud-exporter",
-  "categories": [
-    9
-  ],
-  "date_created": "2025-12-17",
-  "type": "addon",
-  "updateable": true,
-  "privileged": false,
-  "interface_port": 9205,
-  "documentation": "https://github.com/xperimental/nextcloud-exporter",
-  "website": "https://github.com/xperimental/nextcloud-exporter",
-  "logo": "https://cdn.jsdelivr.net/gh/selfhst/icons@main/webp/nextcloud.webp",
-  "config_path": "/etc/nextcloud-exporter.env",
-  "description": "Prometheus exporter for Nextcloud servers. ",
-  "install_methods": [
-    {
-      "type": "default",
-      "script": "tools/addon/nextcloud-exporter.sh",
-      "resources": {
-        "cpu": null,
-        "ram": null,
-        "hdd": null,
-        "os": null,
-        "version": null
-      }
-    }
-  ],
-  "default_credentials": {
-    "username": null,
-    "password": null
-  },
-  "notes": []
-}