[Refactor] Remove dead legacy pipeline.yaml loader and duplicate diff… (#4023)

Signed-off-by: dph97 <nenbaying@163.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: zhuhonghan <z00806815@china.huawei.com>

docs/api/README.md

@@ -92,7 +92,6 @@ Core scheduling and caching components.
 Configuration classes.
 
 - [vllm_omni.config.model.OmniModelConfig][]
-- [vllm_omni.config.stage_config.ModelPipeline][]
 - [vllm_omni.config.stage_config.StageConfig][]
 - [vllm_omni.config.stage_config.StageConfigFactory][]
 - [vllm_omni.config.stage_config.StageType][]