feat(broker): Explicit network id

[teogeb]

Based on https://github.com/streamr-dev/network/pull/1034

Remove networkId command line option from broker bin script. It is most likely not needed, because it has been broken since https://github.com/streamr-dev/network/pull/309. It was originally added in https://github.com/streamr-dev/broker/pull/51.

Removed also obsolete 2nd argument from createBroker() call. It parameter was added here: https://github.com/streamr-dev/broker/pull/157 and removed here https://github.com/streamr-dev/broker/pull/182.