Remove unnecessary email regexp

This is now handled by the admin gem itself, in the JS layer:
alphagov/govuk_admin_template#121

app/helpers/admin/analytics_helper.rb

@@ -4,15 +4,8 @@ def track_analytics_data(type, message)
       {
         'module' => 'auto-track-event',
         'track-action' => "alert-#{type}",
-        'track-label' => flash_text_without_email_addresses(message),
+        'track-label' => strip_tags(message),
       }
     end
-
-    def flash_text_without_email_addresses(message)
-      text_message = strip_tags(message)
-
-      # redact email addresses so they aren't passed to GA
-      text_message.gsub(/\S+@\S+/, '[email]')
-    end
   end
 end