Remove agent forwarding from ci-new SSH config
Remove agent forwarding from ci-new SSH config

Agent forwarding is undesirable because it exposes the use of your private
keys to other people that have root access to the remote machines. It's not
required when using `ProxyCommand` for a jumpbox like this.

alphagov/gds-boxen,alphagov/gds-boxen,alphagov/gds-boxen