Update langchain.chains.create_extraction_chain_pydantic to parse results successfully (#6887)

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- Description: 
- The current code uses `PydanticSchema.schema()` and
`_get_extraction_function` at the same time. As a result, a response
from OpenAI has two nested `info`, and
`PydanticAttrOutputFunctionsParser` fails to parse it. This PR will use
the pydantic class given as an arg instead.
- Issue: no related issue yet
- Dependencies: no dependency change
- Tag maintainer: @dev2049
- Twitter handle: @shotarok28

langchain/chains/openai_functions/extraction.py

@@ -78,9 +78,9 @@ def create_extraction_chain_pydantic(
     class PydanticSchema(BaseModel):
         info: List[pydantic_schema]  # type: ignore
 
-    openai_schema = PydanticSchema.schema()
+    openai_schema = pydantic_schema.schema()
     openai_schema = _resolve_schema_references(
-        openai_schema, openai_schema["definitions"]
+        openai_schema, openai_schema.get("definitions", {})
     )
 
     function = _get_extraction_function(openai_schema)