fix: Remove unused type: ignore comments for mypy

The type: ignore comments were only needed when the except block
executes, but CI runs with LangChain 1.0+ so the try block succeeds.
Mypy flags these as unused-ignore errors.

Author: andrewm4894

posthog/ai/langchain/callbacks.py

@@ -26,8 +26,8 @@
     from langchain_core.agents import AgentAction, AgentFinish
 except (ImportError, ModuleNotFoundError):
     # Fallback for older LangChain versions
-    from langchain.callbacks.base import BaseCallbackHandler  # type: ignore
-    from langchain.schema.agent import AgentAction, AgentFinish  # type: ignore
+    from langchain.callbacks.base import BaseCallbackHandler
+    from langchain.schema.agent import AgentAction, AgentFinish
 from langchain_core.documents import Document
 from langchain_core.messages import (
     AIMessage,