Delete unused networks

Filters to process on the prune list, encoded as JSON (a map[string][]string).

Available filters:

• until=<timestamp> Prune networks created before this timestamp. The <timestamp> can be Unix timestamps, date formatted timestamps, or Go duration strings (e.g. 10m, 1h30m) computed relative to the daemon machine’s time.
• label (label=<key>, label=<key>=<value>, label!=<key>, or label!=<key>=<value>) Prune networks with (or without, in case label!=... is used) the specified labels.