Moved facets from group search to facet query [PD-722]

All tests pass.
Line is copied+pasted from original function, but the basic behavior is if the results of `prod_facets_for_sites()`, which filters on `show_production==1` and `settings.SITE_ID` returns no results, it means there are no custom facets for a site so just go ahead and skip the rest of the function because the solr query is a waste of time.