- remove no longer used ru/lopcomm/supervision.jinja2.py
- restore removed `+ keep on touching RU watchdog` comment.
  Now it relates to ru/lopcomm/stats which became responsible for this function.
- move code of RU-netconf-connection promise to be located nearby stats service
  because this promise interacts with that service, and grouping code by
  interaction makes it easier to understand for humans. Previously
  RU-netconf-connection was interacting with supervision service whcsh is gone
  after the patch in question.
- use double vertical space to delimit logical sections from each other.

open questions:

- before the patch in question stats code was reconnecting after each error
  with 10 seconds pause. Now it logs it wants to reconnect but does _not_
  because top-level `while True` was removed. Was that intended?

  If it was not the intent then new stats code will fail after any single error
  and won't reconnect to RU by itself.

/reviewed-by @lu.xu
/reviewed-on nexedi/slapos!1483