Remove bandaid fix for duplicate linelists once upstream fix is available

[AlexHls]

Describe the bug

#2443 Introduces a bandaid fix for duplicate entries in the atomic database. Since this is a carsus issue we only throw a warning and remove duplicate entries alltogether. Once an upstream fix is available, the warning should be replaces and instead an error should be raised.

tardis/plasma/properties/atomic.py:472

if level_idxs2line_idx.index.duplicated().any():
    logger.warn(
        "Duplicate indices in level_idxs2line_idx. "
        "Dropping duplicates. "
        "This is an issue with the atomic data & carsus. "
        "Once fixed upstream, this warning will be removed. "
        "This will raise an error in the future instead. "
        "See https://github.com/tardis-sn/carsus/issues/384"
    )
    # This is necessary since pd.DataFrame.drop_duplicates()
    # does not remove duplicates if the data is different
    # and only the index is duplicated. See the example given
    # in the pandas documentation:
    # https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.drop_duplicates.html
    level_idxs2line_idx = level_idxs2line_idx[
        ~level_idxs2line_idx.index.duplicated()
    ]