Remove hard-coded model overrides from Together and Groq examples

Prefer service defaults — the hard-coded models we were using are no
longer available on these providers.

examples/foundational/55zzb-update-settings-groq-llm.py

@@ -62,7 +62,6 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
     llm = GroqLLMService(
         api_key=os.getenv("GROQ_API_KEY"),
         settings=GroqLLMService.Settings(
-            model="meta-llama/llama-4-maverick-17b-128e-instruct",
             system_instruction="You are a helpful assistant in a voice conversation. Your responses will be spoken aloud, so avoid emojis, bullet points, or other formatting that can't be spoken. Respond to what the user said in a creative, helpful, and brief way.",
         ),
     )