fix: remove VPN backup (service not running)

Removed VPN backup configuration since the VPN service is not currently
included in the compose.yaml and the vpn_etc_wireguard volume doesn't exist.

Kept Netdata backup as those volumes exist and the service is running.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

restic/compose.yaml

@@ -35,7 +35,6 @@ services:
       - backup_vaultwarden_data:/volumes/vaultwarden_data:ro
       - backup_joplin_data:/volumes/joplin_data:ro
       - backup_jelly_config:/volumes/jelly_config:ro
-      - backup_vpn_etc_wireguard:/volumes/vpn_etc_wireguard:ro
       - backup_netdata_config:/volumes/netdata_config:ro
 
     environment:
@@ -136,9 +135,6 @@ volumes:
   backup_jelly_config:
     name: jelly_config
     external: true
-  backup_vpn_etc_wireguard:
-    name: vpn_etc_wireguard
-    external: true
   backup_netdata_config:
     name: netdata_config
     external: true