Keep only the 5 most recent notebooks in index.md

Remove 6th entry as requested by reviewer to maintain only the last 5 added notebooks in the list.

Author: behroozazarkhalili

notebooks/en/index.md

@@ -12,7 +12,6 @@ Check out the recently added notebooks:
 - [Fine-tuning LLMs for Function Calling with the xLAM Dataset](function_calling_fine_tuning_llms_on_xlam)
 - [Post training an VLM for reasoning with GRPO using TRL](fine_tuning_vlm_grpo_trl)
 - [TRL GRPO Reasoning with Advanced Reward](trl_grpo_reasoning_advanced_reward)
-- [Fine-Tuning a Vision Language Model with TRL using MPO](fine_tuning_vlm_mpo)
 
 You can also check out the notebooks in the cookbook's [GitHub repo](https://github.com/huggingface/cookbook).