Delete a document previously uploaded for this customer, e.g. to replace
a document uploaded in error. The document no longer appears in the
customer files array, no longer satisfies onboarding document
requirements, and can no longer be referenced from a payout's file_ids.
Documents already submitted with an onboarding are not withdrawn from it.

A document that backs a payout cannot be deleted
(400 FILE_ALREADY_USED). Deleting an unknown or already-deleted
document, or one that belongs to another customer, returns
404 NOT_FOUND. No Idempotency-Key is required; a repeated delete
returns 404.