artist urls: stop using normalized_url.

Stop the last remaining uses of the `artist_urls.normalized_url` column.
It's already no longer used by the artist finder. The only remaining
uses were by API users. Those users should use the `url` column instead.

test/functional/artists_controller_test.rb

@@ -184,7 +184,6 @@ class ArtistsControllerTest < ActionDispatch::IntegrationTest
           should respond_to_search(has_urls: "true").with { [@artgerm, @masao] }
           should respond_to_search(has_urls: "false").with { [@banned, @deleted, @artist] }
           should respond_to_search(urls: {url: "https://www.pixiv.net/users/32777"}).with { @masao }
-          should respond_to_search(urls: {normalized_url: "http://www.deviantart.com/artgerm/"}).with { @artgerm }
         end
       end
     end