docs: drop nonexistent 'context' param from RealtimeRunner.__init__ docstring

[vidigoat]

Summary

RealtimeRunner.__init__ only accepts starting_agent, model, and config:

def __init__(
    self,
    starting_agent: RealtimeAgent,
    *,
    model: RealtimeModel | None = None,
    config: RealtimeRunConfig | None = None,
) -> None:

But its docstring's Args: block also lists context: The context to use for the session. — that parameter actually belongs to the separate run() method below it (async def run(self, *, context=..., model_config=...)). It's a copy-paste leftover that documents a parameter __init__ doesn't take.

This drops the stale line so the Args: block matches the signature. Docstring-only; no code or behavior change.

Test plan

No runtime impact (comment-only). Module still parses; the documented args now exactly match __init__'s signature.