[FIX] mail: use correct redirect action

The redirect action to the inbox was removed, but the tests (and the default action
method) need to be updated.

addons/mail/models/mail_thread.py

@@ -504,7 +504,7 @@ class MailThread(models.AbstractModel):
         """ When redirecting towards the Inbox, choose which action xml_id has
             to be fetched. This method is meant to be inherited, at least in portal
             because portal users have a different Inbox action than classic users. """
-        return 'mail.mail_message_action_inbox'
+        return 'mail.mail_channel_action_client_slack'
 
     @api.multi
     def _notification_link_helper(self, link_type, **kwargs):

addons/mail/views/mail_channel_views.xml

@@ -184,10 +184,6 @@
 
 
 
-
-
-    <!-- TODO JEM : SLACK test client action-->
-
     <record id="mail_channel_action_client_slack" model="ir.actions.client">
             <field name="name">Chat</field>
             <field name="tag">mail.chat.instant_messaging</field>