rpc: Remove llm module in favor of zed_llm_client (#28900)

This PR removes the `llm` module of the `rpc` crate in favor of using
the types from the `zed_llm_client`.

Release Notes:

- N/A

crates/rpc/src/rpc.rs

@@ -1,14 +1,12 @@
 pub mod auth;
 mod conn;
 mod extension;
-mod llm;
 mod message_stream;
 mod notification;
 mod peer;
 
 pub use conn::Connection;
 pub use extension::*;
-pub use llm::*;
 pub use notification::*;
 pub use peer::*;
 pub use proto;