[WIP RAG] Finalize RAG parallel
finalizing RAG in parallel to https://github.com/huggingface/transformers/pull/6813
https://github.com/huggingface/transformers/blob/60c8defa01049b559933ad4e2ab3cc32c8b7ef27/src/transformers/tokenization_rag.py#L58

Hello, thank you for the great work! It seems like the first argument passed to the method, `self`, needs to be deleted.<|||||>Closing this PR as it served its purpose. Continue PR together with @ola13 here: https://github.com/huggingface/transformers/pull/6813