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
```

docs/example-config.md

@@ -49,9 +49,6 @@ model_verbosity = "medium"
 # Force-enable reasoning summaries for current model (default: false)
 model_supports_reasoning_summaries = false
 
-# Force reasoning summary format: none | experimental (default: none)
-model_reasoning_summary_format = "none"
-
 ################################################################################
 # Instruction Overrides
 ################################################################################