refactor: remove outdated skills and references from MLOps

- Deleted the `huggingface-accelerate` skill documentation, which included details on distributed training and common workflows.
- Removed `custom-plugins.md`, `megatron-integration.md`, `performance.md`, and other related reference documents that were no longer relevant or necessary.
- This cleanup aims to streamline the MLOps skills repository and improve maintainability.

skills/mlops/pytorch-fsdp/references/index.md

@@ -1,7 +0,0 @@
-# Pytorch-Fsdp Documentation Index
-
-## Categories
-
-### Other
-**File:** `other.md`
-**Pages:** 15