[IMP] account,l10n_generic_coa: add taxes to demo invoice and remove pdf

Task 2206499

We have to call the onchanges manually in order to compute the taxes
We don't want pdf's because they are not consistent with the data.
* Generated pdf would depend on the company details, set during the
  demo steps
* Generating a pdf would need to be done through a cron because
  wkhtmltopdf needs the web server to be running at install time, which
  is not the case. This has been judged too complicated and not worth.
* Hard coded pdf would also depend on the l10n, the date.

closes odoo/odoo#53279

X-original-commit: c41cedef8f0a75ad795a7bd22f96f990e3f0d483
Signed-off-by: Quentin De Paoli (qdp) <qdp@openerp.com>