Hide additional fields for countries with one region

At the moment with countryies with on region there are two places you
can put this information, which is confusing. Instead we should hide it
to encourage users to use the region.

app/views/support_interface/countries/edit.html.erb

@@ -30,7 +30,9 @@
     <%= f.govuk_radio_button :has_regions, :false, label: { text: "No" } %>
   <% end %>
 
-  <%= render "shared/support_interface/country_region_information_fields", f: %>
+  <% if @country.regions.count > 1 %>
+    <%= render "shared/support_interface/country_region_information_fields", f: %>
+  <% end %>
 
   <%= f.govuk_submit "Preview", name: "preview", value: "true" do %>
     <%= f.govuk_submit "Save", name: "preview", value: "false", secondary: true %>