FP3: Use proper source:dest in proprietary files list

This change reflects the fact that we have moved a lot of blobs out
of the `system` folder into `product`. As a result users can now
call our device-specific `extract-files.sh` script on a mounted stock
OTA dump to populate the `vendor/fairphone/FP3` folder.

Change-Id: I05e008ab153eb7f50c3ca2a8e07ace4403588cdc