[FIX] account: avoid double unlinking

With l10n_mx installed:
- Check in the settings that cash basis option is activated, and enabled
on a Purchase Tax (example : IVA(16%) COMPRAS)
- Create a vendor bill with this tax, validate it and
register payment.
- Create a credit note to this invoice, validate and register payment.
- Cancel the credit note

Error will occur, a record is already deleted.
This occur because the canceling action recursively find every related
move to delete, but in the process an account.full.reconcile is going to
be unlinked twice: a check on reverse the exchange rate entry will
trigger the error because the record is already deleted

opw-2199093

closes odoo/odoo#47341

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>