Don't import Bouncer-related Hits

When a site has transitioned, Bouncer serves up:
* assets to make the 404 and 410 pages look nice
* /robots.txt and /sitemap.xml

It also receives requests for /favicon.ico because web browsers.

All of these appear under a site's "Analytics" in the app, but they are not paths that were on the old site and are a distraction. You can't do anything with these hits.

I haven't written a migration to clean up existing data because at the moment we're happy to drop the database at deploy-time. The return on investment just didn't seem to be there.