Removes duplicated call from langchain/client/langchain.py (#5449)

This removes duplicate code presumably introduced by a cut-and-paste
error, spotted while reviewing the code in
```langchain/client/langchain.py```. The original code had back to back
occurrences of the following code block:

```
        response = self._get(
            path,
            params=params,
        )
        raise_for_status_with_text(response)
```

langchain/client/langchain.py

@@ -249,11 +249,6 @@ def read_session(
             params=params,
         )
         raise_for_status_with_text(response)
-        response = self._get(
-            path,
-            params=params,
-        )
-        raise_for_status_with_text(response)
         result = response.json()
         if isinstance(result, list):
             if len(result) == 0: