refactor: use global setting for Vercel Edge runtime

apps/website/src/routes/api/newsletter/+server.ts

@@ -1,9 +1,6 @@
 import { NEWSLETTER_API_TOKEN, NEWSLETTER_LIST_ID } from '$env/static/private'
 import type { RequestHandler } from './$types'
 
-export const config = {
-    runtime: 'edge'
-}
 
 export const POST = (async ({ request, fetch }) => {
     const data: { email: string } = await request.json()