[FIX] mail: activities of archived records

- Create an activity for a crm lead
- Set the lead as lost

The activity still appears in the list.

A proper fix would be to have an `active` field on `mail.activity`. In
the meantime, simply delete activites when archiving.

opw-1817703

addons/mail/models/mail_activity.py

@@ -317,6 +317,15 @@ class MailActivityMixin(models.AbstractModel):
     def _search_activity_summary(self, operator, operand):
         return [('activity_ids.summary', operator, operand)]
 
+    @api.multi
+    def write(self, vals):
+        # Delete activities of archived record.
+        if 'active' in vals and vals['active'] is False:
+            self.env['mail.activity'].sudo().search(
+                [('res_model', '=', self._name), ('res_id', 'in', self.ids)]
+            ).unlink()
+        return super(MailActivityMixin, self).write(vals)
+
     @api.multi
     def unlink(self):
         """ Override unlink to delete records activities through (res_model, res_id). """