Don't pass EF to chroma (#13085)

- **Description:** 

Recently Chroma rolled out a breaking change on the way we handle
embedding functions, in order to support multi-modal collections.

This broke the way LangChain's `Chroma` objects get created, because we
were passing the EF down into the Chroma collection:
https://docs.trychroma.com/migration#migration-to-0416---november-7-2023

However, internally, we are never actually using embeddings on the
chroma collection - LangChain's `Chroma` object calls it instead. Thus
we just don't pass an `embedding_function` to Chroma itself, which fixes
the issue.

libs/langchain/langchain/vectorstores/chroma.py

@@ -124,9 +124,7 @@ class Chroma(VectorStore):
         self._embedding_function = embedding_function
         self._collection = self._client.get_or_create_collection(
             name=collection_name,
-            embedding_function=self._embedding_function.embed_documents
-            if self._embedding_function is not None
-            else None,
+            embedding_function=None,
             metadata=collection_metadata,
         )
         self.override_relevance_score_fn = relevance_score_fn