How to remove specific links from all artifacts in RM

I have a requirements management project in DNG full of custom links types.  I have replicated all of these links in the standard link types and would now like to remove all of the custom link values and then eventually remove the custom link types.

I tried exporting all the artifacts to a CSV file (and include the custom link type in the export).  I then edited the CSV file to "blank out" the column associated with the custom link type.  I then went to do an "Import Artifact...", selected my CSV file (that blanked out the custom link column), chose "Update artifacts that match entries, and ignore new entries).

The process completes but the custom link field still contains all of the links.

I know I can delete them one-by-one from the GUI but am looking for a faster more automated way of remove these links.

Does anyone know how to achieve this?  I am running DNG v 6.0.3

Thank you