The tax group model doesn't have a form view leading to a left side
bigger than the right side and some fields showing that we don't
want to see.
Thus, we add a form view and hide the field country_code, that is
not needed here since we already see the country_id.
closesodoo/odoo#101519
Signed-off-by: Olivier Colson (oco) <oco@odoo.com>