[FIX] mail: remove useless custom property from action dict

The `{'infos': 'mail_sent'}` property returned by `action_send_mail()`
was apparently unused, and orginally intended for debugging, according
to its author.

Since previous commit adds a warning for such unknown properties,
removing it entirely keeps the testsuite green. And it's cleaner
than explicitly allowing that extra key, since it's unused.

closes odoo/odoo#63009

X-original-commit: 7c8c5a9cd716d35783734493cbb15b194e7b787c
Signed-off-by: Olivier Dony (odo) <odo@openerp.com>

addons/mail/wizard/mail_compose_message.py

@@ -175,7 +175,7 @@ class MailComposer(models.TransientModel):
     # to ensure the context is passed correctly
     def action_send_mail(self):
         self.send_mail()
-        return {'type': 'ir.actions.act_window_close', 'infos': 'mail_sent'}
+        return {'type': 'ir.actions.act_window_close'}
 
     def send_mail(self, auto_commit=False):
         """ Process the wizard content and proceed with sending the related