Delete obsolete Parquet and DuckDB files
replaces https://github.com/huggingface/datasets-server/issues/1613 and https://github.com/huggingface/datasets-server/issues/980.

When we call `delete_dataset()`, we should remove all the parquet and duckdb files.

And maybe even the `refs/convert/parquet` branch altogether?
Delete obsolete Parquet and DuckDB files: replaces https://github.com/huggingface/datasets-server/issues/1613 and https://github.com/huggingface/datasets-server/issues/980.

When we call `delete_dataset()`, we should remove all the parquet and duckdb files.

And maybe even the `refs/convert/parquet` branch altogether?