Remove reasoning format (#8484)

This isn't very useful parameter. 

logic:
```
if model puts `**` in their reasoning, trim it and visualize the header.
if couldn't trim: don't render
if model doesn't support: don't render
```

We can simplify to:
```
if could trim, visualize header.
if not, don't render
```

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

@@ -5,7 +5,6 @@ use codex_protocol::openai_models::ConfigShellToolType;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ModelPreset;
 use codex_protocol::openai_models::ModelVisibility;
-use codex_protocol::openai_models::ReasoningSummaryFormat;
 use codex_protocol::openai_models::TruncationPolicyConfig;
 use serde_json::json;
 use std::path::Path;
@@ -35,7 +34,6 @@ fn preset_to_info(preset: &ModelPreset, priority: i32) -> ModelInfo {
         truncation_policy: TruncationPolicyConfig::bytes(10_000),
         supports_parallel_tool_calls: false,
         context_window: None,
-        reasoning_summary_format: ReasoningSummaryFormat::None,
         experimental_supported_tools: Vec::new(),
     }
 }