chore: remove all references to PayloadCMS

apps/landing/.env.example

@@ -1,6 +1 @@
-CMS_SECRET=your-very-long-secret-key
-CMS_POSTGRES_URL=postgres://user:password@host:port/database
-CMS_STORAGE_ENDPOINT=https://your-s3-endpoint.com
-CMS_STORAGE_ACCESS_KEY_ID=your-access-key-id
-CMS_STORAGE_SECRET_ACCESS_KEY=your-secret-access-key
-CMS_STORAGE_REGION=ap-southeast-1
+NEXT_PUBLIC_API_URL=