[REF] mail: remove unnecessary headers in notification emails

Several contextual data is added in notification emails in their headers.
We consider as not necessary to put some of them, notably db uid. It should
not be used outside of Odoo and having Odoo-Objects should be sufficient
for people that want to categorize their emails.

addons/mail/models/mail_thread.py

@@ -832,10 +832,8 @@ class MailThread(models.AbstractModel):
         if not self:
             return {}
         self.ensure_one()
-        database_uuid = self.env['ir.config_parameter'].sudo().get_param('database.uuid')
         return {'headers': repr({
             'X-Odoo-Objects': "%s-%s" % (self._name, self.id),
-            'X-Odoo-db-uuid': database_uuid
         })}
 
     @api.model