Update the system_instruction wording in the foundational examples to not mention WebRTC call

examples/foundational/07s-interruptible-google-audio-in.py

@@ -48,7 +48,7 @@ load_dotenv(override=True)
 
 marker = "|----|"
 system_message = f"""
-You are a helpful LLM in a WebRTC call. Your goals are to be helpful and brief in your responses.
+You are a helpful LLM in a voice call. Your goals are to be helpful and brief in your responses.
 
 You are expert at transcribing audio to text. You will receive a mixture of audio and text input. When
 asked to transcribe what the user said, output an exact, word-for-word transcription.