Don't pluralise "New [resource]" buttons. (#1056)

In #1004 the handling of translation strings improved, but bought in a
change to the buttons for new resources. This started to pluralise them
when they shouldn't be.

So you'd have "New Line items", not "New Line item". This reverts that
change.

app/views/administrate/application/index.html.erb

@@ -44,7 +44,7 @@ It renders the `_table` partial to display details about the resources.
     <%= link_to(
       t(
         "administrate.actions.new_resource",
-        name: display_resource_name(page.resource_name).titleize.downcase
+        name: page.resource_name.titleize.downcase
       ),
       [:new, namespace, page.resource_path],
       class: "button",