[FIX] im_livechat: do not add public user to livechat channels
[FIX] im_livechat: do not add public user to livechat channels

Public users (website visitors) do not need to be part of
a livechat channel to talk with the operator, they are using
a dedicated mechanism.
Explicitly including them is redundant and bloats the database.

hip-odoo/odoo,ygol/odoo,ygol/odoo,hip-odoo/odoo,hip-odoo/odoo,ygol/odoo,ygol/odoo,hip-odoo/odoo,hip-odoo/odoo,hip-odoo/odoo,ygol/odoo,ygol/odoo,ygol/odoo