You can also just leave the pool as was and start the array without any assigned devices there, there won't won't be any errors and next time you just need to re-assign the same devices to that pool and Unraid will import it, you do need to start/stop the array to remove it though.
I didn't delete the entry, just hid it since I though it was no longer needed, but it's now visible again.
https://forums.unraid.net/topic/46802-faq-for-unraid-v6/?do=findComment&comment=462135