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/tui/src/chatwidget/tests.rs

@@ -2749,7 +2749,7 @@ fn active_blob(chat: &ChatWidget) -> String {
 fn get_available_model(chat: &ChatWidget, model: &str) -> ModelPreset {
     let models = chat
         .models_manager
-        .try_list_models(&chat.config)
+        .try_list_models()
         .expect("models lock available");
     models
         .iter()