Update toc.yml

Author: deeikele

articles/ai-studio/toc.yml

@@ -10,8 +10,6 @@
     displayName: applied, cognitive, form recognizer
   - name: Azure AI FAQ
     href: faq.yml
-  - name: Region support
-    href: reference/reference-region-support.md
 - name: Quickstarts
   items:
   - name: Hear and speak with chat in the playground