Deprecate unused OpenLlama architecture (#24922)

* Resolve typo in check_repo.py

* Specify encoding when opening modeling files

* Deprecate the OpenLlama architecture

* Add disclaimer pointing to Llama

I'm open to different wordings here

* Match the capitalisation of LLaMA

docs/source/en/model_doc/open-llama.md

@@ -16,6 +16,21 @@ rendered properly in your Markdown viewer.
 
 # Open-Llama
 
+<Tip warning={true}>
+
+This model is in maintenance mode only, so we won't accept any new PRs changing its code.
+
+If you run into any issues running this model, please reinstall the last version that supported this model: v4.31.0.
+You can do so by running the following command: `pip install -U transformers==4.31.0`.
+
+</Tip>
+
+<Tip warning={true}>
+
+This model differs from the [OpenLLaMA models](https://huggingface.co/models?search=openllama) on the Hugging Face Hub, which primarily use the [LLaMA](llama) architecture.
+
+</Tip>
+
 ## Overview
 
 The Open-Llama model was proposed in [Open-Llama project](https://github.com/s-JoL/Open-Llama) by community developer s-JoL.