当所有的采购流程结束， 为了如存档之类目的PO必须能够被删除。
目前从MM-PUR角度没有一个标准的设置或方法能够阻止在完全收货和发票校验后PO被删除。如需该功能，需要对标准系统/功能做修改或增强。 可查看BAdI ME_PROCESS_PO_CUST
When all the procurement process is finished, it must be possible to delete the PO item， for example for archiving purpose.
As we have already fully received the goods and posted the invoice, the deletion of the item shall have no effect. The procurement process has been completed.
The item shall be marked as deleted, but not actually removed from the system
There is no settings which would not allow delete a PO after GR/IR in standard system.
