chore: rm remote models fflag (#11699)

rm `remote_models` feature flag.

We see issues like #11527 when a user has `remote_models` disabled, as
we always use the default fallback `ModelInfo`. This causes issues with
model performance.

Builds on #11690, which helps by warning the user when they are using
the default fallback. This PR will make that happen much less frequently
as an accidental consequence of disabling `remote_models`.

codex-rs/mcp-server/tests/suite/codex_tool.rs

@@ -507,7 +507,6 @@ request_max_retries = 0
 stream_max_retries = 0
 
 [features]
-remote_models = false
 "#
         ),
     )