Here is one method from the Knowledgebase
1. Recycle the file depots that are using DFMF
2. "Right-click" on the device that contains the filedepot
3. Remove the check for "Use distributed file media format"
4. Perform a backup using this library, this will delete the old file depots.
5. The backup job will create at least one file depot, then recycle and export it/them (this time the .fd is created without the DFMF functionality)
6. Now the pool is clean, you can delete the pool and the file library.