feat: rm the hardcoded invoice types

packages/types/src/freight/index.ts

@@ -151,14 +151,6 @@ export enum InvoiceSource {
   Demurrage = "demurrage",
 }
 
-/**
- * What an invoice bills for within its source — the discriminator when one
- * entity carries several invoices (e.g. a booking's up-front vs final charge).
- */
-export enum InvoiceType {
-  Prepaid = "PREPAID",
-}
-
 export enum SchedulingStatus {
   NotScheduled = "NOT_SCHEDULED",
   Holding = "HOLDING",