Remove duplicate lines (#7138)

I believe these two lines are unnecessary, the variable `function_call`
is already defined.

langchain/agents/openai_functions_agent/base.py

@@ -108,7 +108,6 @@ def _parse_ai_message(message: BaseMessage) -> Union[AgentAction, AgentFinish]:
     function_call = message.additional_kwargs.get("function_call", {})
 
     if function_call:
-        function_call = message.additional_kwargs["function_call"]
         function_name = function_call["name"]
         try:
             _tool_input = json.loads(function_call["arguments"])

langchain/agents/openai_functions_multi_agent/base.py

@@ -107,7 +107,6 @@ def _parse_ai_message(message: BaseMessage) -> Union[List[AgentAction], AgentFin
     function_call = message.additional_kwargs.get("function_call", {})
 
     if function_call:
-        function_call = message.additional_kwargs["function_call"]
         try:
             tools = json.loads(function_call["arguments"])["actions"]
         except JSONDecodeError: