Add a test to test the data fingerprint feature make me realize it was broken.
The code was relying in the distinction between empty and null QByteArray,
but this was a bad idea as this difference is lost when going through QString.
We were removing the wholme journal db when the user wanted to keep all files,
But that would also remove the selective sync lists.
We should only remove the metadata table.
Issue #5484
Camila San