You have received some great advice down below I am sorry I wasn't sure about how to remove it at all. But it is not necessary to leave a website.

Mary

Thank you bicarmee for posting your question. it has helped me although I have not experienced that problem as yet. The answers are very helpfull to me so I am greatful.
Keep up the good work.

But like MiaL said it doesn’t look like the website is ever required. If it were required it would have the little Star next to it on your page.

Login to your WordPress, go to settings, then discussion, and they are you will see some options to check or uncheck for whether or not to make email, website, or name required for commenters.

The website field is not usually mandatory. Whilst it appears I’ve never seen a site where it is mandatory. Have you checked if it is a mandatory field?