update FAQ; custom domain is GA and not public preview

Author: kengaderdus

articles/active-directory-b2c/TOC.yml

@@ -633,6 +633,7 @@
     href: https://azure.microsoft.com/roadmap/?category=security-identity
   - name: Frequently asked questions
     href: ./faq.yml
+    displayName: FAQ
   - name: Getting help
     href: ../active-directory/develop/developer-support-help-options.md
   - name: Pricing

articles/active-directory-b2c/faq.yml

@@ -149,7 +149,7 @@ sections:
       - question: |
           Can I use my own URLs on my sign-up and sign-in pages that are served by Azure AD B2C? For instance, can I change the URL from contoso.b2clogin.com to login.contoso.com?
         answer: |
-          This feature is available in public preview. For details, see [Azure AD B2C custom domains](./custom-domain.md?pivots=b2c-user-flow).
+          Yes, you can use your own domain. For details, see [Azure AD B2C custom domains](./custom-domain.md?pivots=b2c-user-flow).
           
       - question: |
           How do I delete my Azure AD B2C tenant?