artist_url.rb: remove legacy artist url normalization code.

* `legacy_normalize` came from c6012535, which is no longer a problem.

* `normalize_for_search` is only used for "[mass edit]" links
in artist entries. These links are a shortcut for performing a
`-artist_name source:<artist_url> -> artist_name` mass edit to tag
untagged artists, but this won't work for most sites these days.

app/views/artists/_summary.html.erb

@@ -33,9 +33,6 @@
             <% else %>
               <del><%= h(url.url) %></del>
             <% end %>
-            <% if CurrentUser.user.is_moderator? %>
-              [<%= link_to("mass edit", edit_moderator_tag_path(:antecedent => "-#{artist.name} source:#{ArtistUrl.normalize_for_search(url.url)}", :consequent => artist.name)) %>]
-            <% end %>
           </li>
         <% end %>
       </ul>