Server registration and stats reporting has been removed from what was
once http://enterprise.influxdata.com. The app that lived there, now
runs at http://usage.influxdata.com, so that the subdomain can
eventually be repurposed. Because we also want to repurpose the
`enterprise-client` repo, we have also renamed that to `usage-client`.
InfluxDB no longer needs the `registration` service now, since all of
the endpoints it communicates with simply discard the data provided to
them.
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