docs: update document examples (#31006)
## Description:
As I was following the docs I found a couple of small issues on the
docs.
this fixes some unused imports on the [extraction
page](https://python.langchain.com/docs/tutorials/extraction/#the-extractor)
and updates the examples on [classification
page](https://python.langchain.com/docs/tutorials/classification/#quickstart)
to be independent from the chat model.
