Delete retrieval directory

retrieval/BM25/BM25.sh

retrieval/BM25/generate_BM25.py

retrieval/LongBench.py

retrieval/README.md

retrieval/contriever/LB2mC.py

retrieval/contriever/generate_passage_embeddings.py

retrieval/contriever/mContriever.sh

retrieval/contriever/merge_output.py

retrieval/contriever/passage_retrieval.py

retrieval/embedding/generate_openai_embedding.py

retrieval/embedding/openai_embedding.sh

retrieval/eval.py

retrieval/pred.py

retrieval/requirements.txt

retrieval/splitter.py