Remove RAG tutorial

Author: bojunehsu

articles/ai-services/content-understanding/toc.yml

@@ -93,9 +93,6 @@ items:
     - name: Create a custom analyzer
       displayName: custom, analyzer, document, text, images, video, audio, multimodal, visual, structured, content, field, extraction
       href: tutorial/create-custom-analyzer.md 
-    - name: Build a retrieval-augmented solution
-      displayName: RAG, retrieval, augmented, generation, knowledge, base, search, index, vector
-      href: tutorial/build-rag-solution.md
     - name: Build a person directory
       displayName: person, directory, search, index, vector
       href: tutorial/build-person-directory.md