What hosts the NFS server you previously mounted? If the retention policy doesnt have the mount to clean up after itself you'll have to do it manually.
Agreed with Jon. If you have now removed the VM from vmPRO's control, it's not going to execute it's retention policy and delete the old backups for you.
So, manually delete them yourself from the NFS mount. Basically, vmPRO isn't controlling the data once you remove the VM from the backup / retention policy.
All the VM backups will be located in a directory on the NFS share named after the vSphere server or ESX server where the VM was residing when backed up. Should be easy enough to find.