Hello there, @info1358.
I'd be glad to help you remove your customer in the list.
The option to delete the customer is unavailable. Although, you can make them inactive. Here's how:
I've added this article for your future reference about managing your customer's charges: Delete customer with unbilled charges.
Feel free to reply in the comment section below if you have other questions. I'd be happy to answer them for you. Have a wonderful day ahead.