Update use-server.mdx remove "at least" (#1187)

Author: klequis

src/routes/solid-start/reference/server/use-server.mdx

@@ -11,7 +11,7 @@ const logHello = async (message: string) => {
 };
 ```
 
-**Note:** `"use server"` functions must be marked async or at least return a promise.
+**Note:** `"use server"` functions must be marked async or return a promise.
 
 ## Basic usage