Remove incorrect statement about the disabled attribute on `<form>`

Created by: tobyzerner

You can disable every form element within a form with the disabled attribute on the <form>.

I really want to be mistaken, because this would be a very useful feature! But I don't believe it's true. I can't find anything about this on MDN Web Docs, and adding the disabled attribute to a <form> does nothing on any browser in my testing.

The disabled attribute on a <fieldset> does disable all descendant form controls – perhaps that's where the mixup has come from.