Reference new tcp-agent-listener endpoint

[daniel-beck]

trafficstars

Downstream of https://github.com/jenkinsci/jenkins/pull/5495

It is unclear to me what the compatibility requirements of remoting are. This is a very simple patch that assumes remoting can be older (~minimum version defined in core), but never newer.

Also noting two TODOs where further cleanup can be done once https://github.com/jenkinsci/jenkins/pull/5494 is released or developer documentation migrated away from the wiki.