Don't rely on tools for structured outputs if there's no structure to the output

[shreyashankar]

If the output schema is just one key with string type value (E.g., answer: string), then we don't need to use tool calling to get a structured output from the LLM. We can just query the LLM normally and save the output string to the specified key (e.g., answer). This will increase success a lot for open-source LLMs.