[IMP] website_mail : remove 'website_message_ids' from mail.thread

This inheritance wasn't working till the commit of rco, modifying
models inheritance.
Anyway, `website_message_ids` field is already defined on several
models (product, slide, forum questions, blog post, ...), and each
of them have a different domain attribute.
So making the mail.thread mixin providing this field is not so
interessting since it will be overrided for specific behavior.
We remove this field as it can't be usefull and generic.

addons/website_mail/models/__init__.py

@@ -2,5 +2,4 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 import mail_message
-import mail_thread
 import update

addons/website_mail/models/mail_thread.py

@@ -1,13 +0,0 @@
-# -*- coding: utf-8 -*-
-# Part of Odoo. See LICENSE file for full copyright and licensing details.
-
-from odoo import fields, models
-
-
-# TODO for trunk, remove me
-class MailThread(models.AbstractModel):
-    _inherit = 'mail.thread'
-
-    website_message_ids = fields.One2many('mail.message', 'res_id',
-        domain=lambda self: ['&', ('model', '=', self._name), ('message_type', '=', 'comment')],
-        string='Website Messages', help="Website communication history")

addons/website_sale/models/product.py

@@ -75,7 +75,6 @@ class ProductTemplate(models.Model):
     _name = 'product.template'
     _mail_post_access = 'read'
 
-    # TODO FIXME tde: when website_mail/mail_thread.py inheritance work -> this field won't be necessary
     website_message_ids = fields.One2many(
         'mail.message', 'res_id',
         domain=lambda self: ['&', ('model', '=', self._name), ('message_type', '=', 'comment')],