Remove hard-coded fallback to English locale

In production mode the English locale is always used as fallback.
In development mode there is currently no fallback, so the English
locale isn't loaded and the second call to I18n.l() fails too.

app/mailers/user_notifications.rb

@@ -41,11 +41,8 @@ class UserNotifications < ActionMailer::Base
     build_email( user.email, template: "user_notifications.account_created", email_token: opts[:email_token])
   end
 
-  # On error, use english
   def short_date(dt)
     I18n.l(dt, format: :short)
-  rescue I18n::MissingTranslationData
-    I18n.l(dt, format: :short, locale: 'en')
   end
 
   def digest(user, opts={})