Delete cache and assets for non existent datasets
Related to https://github.com/huggingface/datasets-server/issues/1285 and https://github.com/huggingface/datasets-server/issues/1284
This PR will fix only the obsolete cache by non existent datasets, the ones related to obsolete configs/splits will be treated in another PR

Delete cache and assets for non existent datasets: Related to https://github.com/huggingface/datasets-server/issues/1285 and https://github.com/huggingface/datasets-server/issues/1284
This PR will fix only the obsolete cache by non existent datasets, the ones related to obsolete configs/splits will be treated in another PR
