[IMP] sale(_management): remove the useless colspan

In e2e27b41 variable `colspan` and several `<t t-set="colspan"/>` were
removed replacing `t-att-colspan="colspan"` with `colspan="99"`.

but due to xpath behaviour reveted in commit https://github.com/odoo/odoo/commit/a540f7864af5fd46cc30ea8c99b2f404cbf58dd7
so now in master remove the useless colspan code.

task-2002587
closes: #34009