Remove the File concept

[xweichu]

No description provided.

[jlefevre]

I recommend that we keep the file abstraction info. This is just metadata and an API, therefore users are not required to use it or access it. But I think it is useful for us internally.

In our system, the files are deconstructed and no longer exist. Thus the file info is required to query or reconstruct the "original" datasets if needed in this domain or others. Recovering original data is also useful when exporting data out of our system.