Update internal telemetry endpoint and remove external one
Created by: dadlerj
Fixes https://github.com/sourcegraph/sourcegraph/issues/7288
(This PR is the first piece of https://github.com/sourcegraph/sourcegraph/pull/6473, after it was broken up)
This PR removes the unused external telemetry endpoint on sourcegraph.com (this hasn't been in use for some time now).
This PR also simplifies our internal telemetry API and updates the handler to also use the new usagestats.LogEvent
usage stats endpoint