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/plan_item.rs

@@ -215,10 +215,7 @@ async fn collect_turn_notifications(
 }
 
 fn create_config_toml(codex_home: &Path, server_uri: &str) -> std::io::Result<()> {
-    let features = BTreeMap::from([
-        (Feature::RemoteModels, false),
-        (Feature::CollaborationModes, true),
-    ]);
+    let features = BTreeMap::from([(Feature::CollaborationModes, true)]);
     let feature_entries = features
         .into_iter()
         .map(|(feature, enabled)| {

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]

codex-rs/app-server/tests/suite/v2/thread_resume.rs

@@ -1008,7 +1008,6 @@ sandbox_mode = "read-only"
 model_provider = "mock_provider"
 
 [features]
-remote_models = false
 personality = true
 
 [model_providers.mock_provider]
@@ -1038,7 +1037,6 @@ sandbox_mode = "read-only"
 model_provider = "mock_provider"
 
 [features]
-remote_models = false
 personality = true
 
 [model_providers.mock_provider]

codex-rs/app-server/tests/suite/v2/turn_start.rs

@@ -1871,7 +1871,7 @@ fn create_config_toml_with_sandbox(
     feature_flags: &BTreeMap<Feature, bool>,
     sandbox_mode: &str,
 ) -> std::io::Result<()> {
-    let mut features = BTreeMap::from([(Feature::RemoteModels, false)]);
+    let mut features = BTreeMap::new();
     for (feature, enabled) in feature_flags {
         features.insert(*feature, *enabled);
     }