Cache directories changed due to recent changes in how config kwargs are handled
Since #2659 I can see weird cache directory names with hashes in the config id, even though no additional config kwargs are passed. For example:

```python
from datasets import load_dataset_builder

c4_builder = load_dataset_builder("c4", "en")
print(c4_builder.cache_dir)
# /Users/quentinlhoest/.cache/huggingface/datasets/c4/en-174d3b7155eb68db/0.0.0/...

# instead of 
# /Users/quentinlhoest/.cache/huggingface/datasets/c4/en/0.0.0/...
```
This issue could be annoying since it would simply ignore old cache directories for users, and regenerate datasets

cc @stas00 this is what you experienced a few days ago
