Remove data from GitHub before archiving

[Aariq]

We don't want to duplicate the data and instead point people to the eventual Dryad archived data from https://github.com/BrunaLab/HeliconiaDataPaper. Need to .gitignore the relevant data files and remove them from GitHub. This is an arduous task, if I remember correctly.

[Aariq]

Could change relevant tar_file() args to tar_url() if Dryad offers permalinks to raw csvs (i doubt it)