Revert "pass the dataset features to the IterableDataset.from_generator"
This reverts commit b91070b9c09673e2e148eec458036ab6a62ac042 (temporarily)

It hurts iterable dataset performance a lot (e.g. x4 slower because it encodes+decodes images unnecessarily). I think we need to fix this before re-adding it

cc @mariosasko @Hubert-Bonisseur 