NativeLCEL example in GenAI tutorial needs update for langchain 1.x

[rblumer4]

In section 6.2 of the GenAI tutorial, there is a ContextualCompressorRetriever example.
That example uses code with langchain.retriever in it:

from langchain.retrievers import ContextualCompressionRetriever
from langchain.retrievers.document_compressors import LLMChainExtractor
from langchain_openai import OpenAI

llm = OpenAI(temperature=0)
compressor = LLMChainExtractor.from_llm(llm)
compression_retriever = ContextualCompressionRetriever(
    base_compressor=compressor, base_retriever=retriever
)

For use with langchain 1.x, that needs to be updated.
At a minium, it needs to be updated to use a different package name: langchain_classic.retrievers