[codex] Remove remote thread store implementation (#21596)

Remove the remote thread-store backend and checked-in protobuf
artifacts. We've moved these into another crate that link against this
one.

Also remove the config settings for thread store backend selection,
since we'll instead pass an instantiated thread store into the core-api
crate's main entrypoint.

codex-rs/thread-store/src/lib.rs

@@ -8,7 +8,6 @@ mod error;
 mod in_memory;
 mod live_thread;
 mod local;
-mod remote;
 mod store;
 mod types;
 
@@ -20,7 +19,6 @@ pub use live_thread::LiveThread;
 pub use live_thread::LiveThreadInitGuard;
 pub use local::LocalThreadStore;
 pub use local::LocalThreadStoreConfig;
-pub use remote::RemoteThreadStore;
 pub use store::ThreadStore;
 pub use types::AppendThreadItemsParams;
 pub use types::ArchiveThreadParams;