Keeping the deletion request itself may actually be necessary to ensure that after you delete the requested data it stays deleted.

I didn't save the link but at least one country's privacy regulator has said that when processing a deletion request you do not have to go through all your backups and remove the data from them too.

If you ever have to do a restore from those backups you will need to re-apply past deletion requests to the restored data before you start using it.