Prefer websockets when providers support them (#13592)

Remove all flags and model settings.

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Co-authored-by: Codex <noreply@openai.com>

codex-rs/app-server/tests/common/models_cache.rs

@@ -45,7 +45,6 @@ fn preset_to_info(preset: &ModelPreset, priority: i32) -> ModelInfo {
         effective_context_window_percent: 95,
         experimental_supported_tools: Vec::new(),
         input_modalities: default_input_modalities(),
-        prefer_websockets: false,
         used_fallback_model_metadata: false,
         supports_search_tool: false,
     }