status: delete unused, incomplete status client & server

The plan was to have a stand-alone status server that just kept track
of the last-reported status updates from various things, and then have
components self-report their status, and then the status server would
report a lack of timely updates as a failure.

But this was never completed and a bunch of health checking went into
the coordinator instead, which kinda works well enough.

I still think this project should be revived, but maybe it could use
some existing cloudy product instead.

In any case, I don't see myself finishing this, so I'm going to delete
this unused code for now. Others can resurrect it if desired if/when
they move stuff out of the coordinator.

Updates golang/go#21315
Updates golang/go#22603

Change-Id: I2d3c33358855206ea98283c9871c6e050e931a43
Reviewed-on: https://go-review.googlesource.com/c/build/+/210740
Reviewed-by: Alexander Rakoczy <[email protected]>
Run-TryBot: Alexander Rakoczy <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: bradfitz