Delete an invoice series

Soft-deletes an invoice series, deactivating it first if it is active.

• The code is not released: it stays taken after the deletion because it identifies the invoices already issued under it, so recreating a series with the same code answers 409 SERIES_CODE_DUPLICATED.
• Default series: it cannot be deleted while another active series of the same document type exists — promote that other one first. If it is the only series of its type it is deleted and the type is left with none, a valid state in which issuing without an explicit series_id answers SERIES_DEFAULT_NOT_FOUND.