Delete fields

Maybe we just need to remove some fields from some records, for example if we are including some field that should not be transmitted.

Just like with the previous case, we just need to add the -F flag with the list of fields to delete. These fields will be deleted from the selected records, or from all records in the file if we don't specify any record.

To indicate the records where the fields will be deleted, we use the -F flag.

We should take care not to delete some mandatory fields as the file surely will be rejected.