Revoke a payment method's wallet credential (payments-api provider contract)

Called when payments-api cancels a saved wallet method or an off_session intent. Finds the method's active instrument, releases the credential at its wallet (Maya: delete the link; GCash: unbind), marks it revoked, and answers the instrument shape; only data.id is read. No active instrument answers success (nothing left to revoke; a repeat lands here). An instrument of another organization or mode is 404. A wallet that refuses answers 502, never 404: payments-api reads 404 as already gone and would record the method revoked over a live binding.