*: account,l10n_account_withholding_tax,l10n_latam_check

Argentina carried its own withholding implementation, written before
l10n_account_withholding_tax existed.
The generic module covers most of the needs today, so the
parallel implementation only means a lot of overhead.

Drop it and keep what the framework cannot know:

- Argentine documents declare no withholding, so what is owed comes
  from the regimes the partner is registered in at the payment date;
- the base restates what those documents declare on the proportion the
  payment settles, on their untaxed or total amount per regime;
- earnings regimes accumulate per ARCA code over the month, against a
  scale and a non-taxable minimum;
- checks fix the net amount handed over, so the gross the withholding
  is levied on has to be searched for.

The taxes now follow the generic convention and hold a negative
amount.

_get_default_withhold is the only part of the generic default the
localization replaces: with nothing declared on the documents, the
mode depends solely on what is left to pay.

Side changes:
- add some minimum validation on the l10n_latam_check module.
- add a generic empty notebook on the payment registration wizard
  to ease overrides.

task-5865443