Revert "[V1] Scatter and gather placeholders in the model runner" (#16075)

docs/source/models/supported_models.md

@@ -989,6 +989,9 @@ See [this page](#generative-models) for more information on how to use generativ
 <sup>+</sup> Multiple items can be inputted per text prompt for this modality.
 
 :::{important}
+To use Gemma3 series models, you have to install Hugging Face Transformers library from source via
+`pip install git+https://github.com/huggingface/transformers`.
+
 Pan-and-scan image pre-processing is currently supported on V0 (but not V1).
 You can enable it by passing `--mm-processor-kwargs '{"do_pan_and_scan": True}'`.
 :::