``get_portal_url`` is already used in portal mixin. As we are in a side module doing things not really related to portal mixin let us inline it directly as it is used only once anyway. Indeed this method does not give any portal url just a base url with a db parameter, used afterwards to let people connect to the db. Task-2712450 (Mail/Sale: Improve 'Pay Now' notification template) closes odoo/odoo#82627 Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>