Only serve statistics publications from /statistics

They were still routable from /publications, as well as /statistics, which is bad.
Serve them from one authoritative place, and support any use of old style with redirects

Removes a couple of old tests for statistics-behaviour on publication views. The first
of which failed when adding the redirect, the 2nd two silently pass, as they're refuting
a selector against an empty body.

https://www.agileplannerapp.com/boards/105200/cards/5540
It's not explicitly defined, it's one of the routing helpers that rails generates based on `resources :publications` in the routes file:

```
$ rake routes | grep publication
                    publications GET    /government/publications(.:locale)(.:format)               publications#index {:locale=>"en"}
                     publication GET    /government/publications/:id(.:locale)(.:format)           publications#show {:locale=>"en"}
     publication_html_attachment GET    /government/publications/:publication_id/:id(.:format)     html_attachments#show
              admin_publications POST   /government/admin/publications(.:format)                   admin/publications#create
           new_admin_publication GET    /government/admin/publications/new(.:format)               admin/publications#new
          edit_admin_publication GET    /government/admin/publications/:id/edit(.:format)          admin/publications#edit
               admin_publication GET    /government/admin/publications/:id(.:format)               admin/publications#show
                                 PUT    /government/admin/publications/:id(.:format)               admin/publications#update
                                 DELETE /government/admin/publications/:id(.:format)               admin/publications#destroy
```