[REM] mail: remove useless link between message and shortcodes

There is a o2m / m2o link between mail.message and mail.shortcode. However
this link is not used: 'messages' (m2o from shortcode to message) is never
set. Anyway there is no usage of this link: shortcodes are replaced in
message body and that's it.

Task-3557985 (Mail: Message cleanup (shortcode, link))
Prepares Task-36879 (Mail: Support MultiCompany Aliases)

Part-of: odoo/odoo#138938

addons/mail/models/mail_message.py

@@ -178,7 +178,6 @@ class Message(models.Model):
     # as the cache value for this inverse one2many is up-to-date.
     # Besides for new messages, and messages never sending emails, there was no mail, and it was searching for nothing.
     mail_ids = fields.One2many('mail.mail', 'mail_message_id', string='Mails', groups="base.group_system")
-    canned_response_ids = fields.One2many('mail.shortcode', 'message_ids', string="Canned Responses", store=False)
     reaction_ids = fields.One2many('mail.message.reaction', 'message_id', string="Reactions", groups="base.group_system")
 
     @api.depends('body', 'subject')

addons/mail/models/mail_shortcode.py

@@ -19,5 +19,4 @@ class MailShortcode(models.Model):
     substitution = fields.Text('Substitution', required=True,
         help="Content that will automatically replace the shortcut of your choosing. This content can still be adapted before sending your message.")
     description = fields.Char('Description')
-    message_ids = fields.Many2one('mail.message', string="Messages", store=False)
     last_used = fields.Datetime('Last Used', help="Last time this shortcode was used")

addons/mail/models/mail_thread.py

@@ -2746,7 +2746,7 @@ class MailThread(models.AbstractModel):
         for values in values_list:
             create_values = dict(values)
             # Avoid warnings about non-existing fields
-            for x in ('from', 'to', 'cc', 'canned_response_ids'):
+            for x in ('from', 'to', 'cc'):
                 create_values.pop(x, None)
             create_values['partner_ids'] = [Command.link(pid) for pid in (create_values.get('partner_ids') or [])]
             create_values_list.append(create_values)

addons/test_mail/tests/test_message_post.py

@@ -499,7 +499,6 @@ class TestMessageNotify(TestMessagePostCommon):
 
         for parameters in [
             {'message_type': 'comment'},
-            {'canned_response_ids': []},
             {'child_ids': []},
             {'mail_ids': []},
             {'notification_ids': []},