deferred_style: only support html notification

bt5/erp5_deferred_style/SkinTemplateItem/portal_skins/erp5_deferred_style_core/ERP5Site_notifyReportComplete.py

@@ -30,15 +30,9 @@ if prefs.getPreferredDeferredReportStoredAsDocument():
     notification_mapping_dict = {
         'report_link_list': report_url_text,
     }
-    if notification_message.getContentType() == "text/html":
     message = notification_message.asEntireHTML(
         safe_substitute=False,
         substitution_method_parameter_dict={'mapping_dict': notification_mapping_dict})
-    else:
-      message_text_format = "text/plain"
-      message = notification_message.asText(
-        safe_substitute=False,
-        substitution_method_parameter_dict={'mapping_dict': notification_mapping_dict})
 
 portal.portal_notifications.activate(activity='SQLQueue').sendMessage(
     recipient=user_name,