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/codex-api/src/endpoint/models.rs

@@ -227,7 +227,6 @@ mod tests {
                     "truncation_policy": {"mode": "bytes", "limit": 10_000},
                     "supports_parallel_tool_calls": false,
                     "context_window": null,
-                    "reasoning_summary_format": "none",
                     "experimental_supported_tools": [],
                 }))
                 .unwrap(),