remove task_arena from lab04

website/lab/04/index.md

@@ -431,7 +431,7 @@ while start_time.elapsed().as_millis() < time_interval {}
 
 You should notice that one of the tasks is not running. Why? (**1p**)
     :::tip
-    Use a different task instance for each LED. You can spawn multiple instances of the same task, however you need to specify the pool size with `#[embassy_executor::task(pool_size = 2)]`. Take a look at [task-arena](https://docs.embassy.dev/embassy-executor/git/std/index.html#task-arena) for more info.
+    Use a different task instance for each LED. You can spawn multiple instances of the same task, however you need to specify the pool size with `#[embassy_executor::task(pool_size = 2)]`.
     Use [`AnyPin`](https://docs.embassy.dev/embassy-stm32/git/stm32u545re/gpio/struct.AnyPin.html) and blinking frequency parameters for the task. 
     :::