rm un-unified datasets and update readme

README.md

convlab/nlu/jointBERT/README.md

data/unified_datasets/commongen/README.md

data/unified_datasets/commongen/data.zip

data/unified_datasets/commongen/dummy_data.json

data/unified_datasets/commongen/preprocess.py

data/unified_datasets/commongen/shuffled_dial_ids.json

data/unified_datasets/dart/README.md

data/unified_datasets/dart/data.zip

data/unified_datasets/dart/dummy_data.json

data/unified_datasets/dart/preprocess.py

data/unified_datasets/dart/shuffled_dial_ids.json

data/unified_datasets/frames/README.md

data/unified_datasets/frames/data.zip

data/unified_datasets/frames/ontology.json

data/unified_datasets/frames/original_data.zip

data/unified_datasets/frames/preprocess.py

data/unified_datasets/multiwoz22/README.md

data/unified_datasets/multiwoz22/data.zip

data/unified_datasets/multiwoz22/ontology.json