[FIX] mail: remove unneeded call to `refresh()`

With new api, this call is not wanted anymore. The cache is cleared
automatically, no need to clear the whole cache; that's a little bit
overkill and reduce performances.

addons/mail/mail_message.py

@@ -879,7 +879,6 @@ class mail_message(osv.Model):
             cr, uid, newid, partners_to_notify=list(partners_to_notify), context=context,
             force_send=force_send, user_signature=user_signature
         )
-        message.refresh()
 
         # An error appear when a user receive a notification without notifying
         # the parent message -> add a read notification for the parent