small changes to profiler

[dafnapension]

• make bluebench_profiler profile any input dataset_query, or a list thereof, including a list of cards. Thus making card_profiler and compare_performance_results (that only dealt with a list of cards) -- unnecessary, hence deleted.
• add a list of explicit split names to the only card that needs it -- prepare/cards/xlsum.py (all the other can retrieve their split names easily, through HF get_dataset_splits_names (or get_dataset_config_info which returns the same)
• small change in docstring of operators.py to eliminate a red line in make docs-server