Use standard locale names for Globalize

It turns out it is not necessary to downcase and underscore
locale names to use the globalize-accessor gem. The gem
will automatically underscore the locale name when defining and
calling the accessor methods.

app/helpers/site_customization_helper.rb

@@ -1,6 +1,6 @@
 module SiteCustomizationHelper
   def site_customization_enable_translation?(locale)
-    I18nContentTranslation.existing_languages.include?(neutral_locale(locale)) || locale == I18n.locale
+    I18nContentTranslation.existing_languages.include?(locale) || locale == I18n.locale
   end
 
   def site_customization_display_translation?(locale)