Before this commit, the livechat was still using a dedicated route to fetch messages on page load. Since [1], visitors are actually mail guest so they can access the classic mail route in order to do so. This commit adapt the livechat code to use this route instead of the custom one. At the same time, this commit simplify the livechat service. part of task-3332628 [1]: https://github.com/odoo/odoo/pull/129770 closes odoo/odoo#133430 Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>