templates: remove gemini_function_agent unused file (#18112)

- [X] Gemini Agent Executor imported `agent.py` has Gemini agent
executor which was not utilised in current template of gemini function
agent 🧑‍💻 instead openai_function_agent has been used


@sbusso  @jarib  please someone review it

---------

Co-authored-by: Erick Friis <erick@langchain.dev>

templates/gemini-functions-agent/main.py

@@ -1,5 +0,0 @@
-from openai_functions_agent.agent import agent_executor
-
-if __name__ == "__main__":
-    question = "who won the womens world cup in 2023?"
-    print(agent_executor.invoke({"input": question, "chat_history": []}))  # noqa: T201