Remove the history of the reference_data from the repository

[flampouris]

The repository is about 250M from which the 240M is the volume of the history due to the reference data that were initially committed to Vlab git.

As this is a new repo, and currently there are only three forks, it will be useful to clean the history related to the specific *.mat files that now are provided through the FTP server.

For anybody interested, I cleaned the history of the master at my gridgen fork. The history is now less than 2M.