Rip out export mode implementation and tests

[mih]

Issues continue to be discovered. I think this is not ready yet, and the inability to export two files with identical content but different names is the final nail on the coffin (tests showing that dataverse can and the implementation here cannot come in #226).

If not solution can be found today, wipe it out.

[mih]

It seems we are on-track to getting it to work cross-platform.