Remove RPC messages pertaining to the LLM token (#36252)

This PR removes the RPC messages pertaining to the LLM token.

We now retrieve the LLM token from Cloud.

Release Notes:

- N/A

Cargo.lock

@@ -3324,7 +3324,6 @@ dependencies = [
  "http_client",
  "hyper 0.14.32",
  "indoc",
- "jsonwebtoken",
  "language",
  "language_model",
  "livekit_api",
@@ -3370,7 +3369,6 @@ dependencies = [
  "telemetry_events",
  "text",
  "theme",
- "thiserror 2.0.12",
  "time",
  "tokio",
  "toml 0.8.20",