docs: change event payload handling in subscribers (#8078)

www/apps/book/app/basics/workflows/page.mdx

@@ -133,7 +133,7 @@ To execute the workflow, invoke it passing the Medusa container as a parameter.
       data,
       container,
     }: SubscriberArgs<{ id: string }>) {
-      const userId = "data" in data ? data.data.id : data.id
+      const userId = data.data.id
       const userModuleService: IUserModuleService = container.resolve(
         ModuleRegistrationName.USER
       )