Remove activeExtensions event
Created by: dadlerj
This event fires a lot — it represents nearly 12% of all events on sourcegraph.com in the last few months. We also (fortunately or not) never followed through on using this information, so it is firing with no purpose.
Additionally, it's not really an event (as no user or server action takes place) — it's just a background logging action that fires periodically, and there are likely better/more idiomatic ways to achieve this that would be worth exploring.
Finally, given fears about overloading postgres with events, and the fact that we can always add it back later, I prefer to simply remove this for now.
CC @ebrodymoore
