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/app-server/tests/suite/v2/review.rs

@@ -437,7 +437,6 @@ sandbox_mode = "read-only"
 model_provider = "mock_provider"
 
 [features]
-remote_models = false
 shell_snapshot = false
 
 [model_providers.mock_provider]