[FIX] l10n_it_fatturapa_pec: Remove extra fields from message

`message_dict` contains values used to track the message, but we use it to create a `mail.message` so the extra values have to be removed because they are not fields of `mail.message`.

l10n_it_fatturapa_pec/models/mail_thread.py

@@ -45,6 +45,7 @@ def clean_message_dict(self, message_dict):
         del message_dict["bounced_partner"]
         del message_dict["bounced_msg_id"]
         del message_dict["bounced_message"]
+        del message_dict["x_odoo_message_id"]
 
     @api.model
     def message_route(