Hi archA,
You can delete them. Just add a rule that sets the original field to blank. The link should be in a separate field, so this should work.
If you need to do a bulk update, our Document Deployer tool may be able to help, but it might require an hour of support to configure to run the batch job.
Otherwise, just have a rule on load that sets the original attachment field to blank if the link is non-blank.
:)