scraper_q: Don't require a restart to fetch new services.

I've received multiple requests from people to confirm why their site
isn't scraping properly despite being set up with embedly. The reason is
the scraper_q wasn't restarted recently and therefore it was still using
an old service list.

Since the service list is memoized, it doesn't really matter if we
"fetch" it on every iteration. This also allows the lookup to be moved
out of the higher layers of the queue which shouldn't have knowledge of
embedly down to the correct place.