fix: vanity domains do not require custom domain addon (supabase#18857)

apps/docs/pages/guides/platform/custom-domains.mdx

@@ -109,7 +109,6 @@ To get started:
 1. [Log in](/docs/guides/resources/supabase-getting-started/local-development#log-in-to-the-supabase-cli) to your Supabase account using the CLI.
 1. Ensure that you have [Owner or Admin permissions](/docs/guides/platform/access-control#manage-team-members) for the project you'd like to set up a vanity subdomain for.
 1. Ensure that your organization is on a paid plan (Pro/Team/Enterprise plan) in the [Billing page of the Dashboard](https://supabase.com/dashboard/org/_/billing).
-1. Ensure that your project has the custom domain add on in the [Add ons page of the Dashboard](https://supabase.com/dashboard/project/_/settings/addons).
 
 ## Configure a Vanity Subdomain