Change the way of filtering columns for Eurostat

[Rafalz13]

"Seems like unnecessary bloat. Pandas already provides a trivial way to filter a DataFrame by columns (df[columns]) and will throw an error if you specify incorrect ones.

As for figuring out what columns are available, if you want to do this with viadot, that can be done by running .to_df(...) without any filters. " - comment #1041 (comment)