Remove building nats from source

[jackonelli]

The latest released version nats-server does not yet support web-sockets, so it needs to be built from the master branch.
This step obviously requires installation of golang, hopefully this feature will soon be on the stable release and a simple download will suffice.
Until then, the NATS server repo is included as a submodule in the BryggIO repo.

According to below issue, this will be around the end of 2020

nats-io/nats-server#1309