remove opinionated scroll preventing behavior

adding overflow hidden to this.$root was assuming too much of it's html markup structure and could create unwanted side effects (like empty scrollbars on non-full-width root divs).

This was added to prevent modal jump, but adding overflow-y: scroll to html is way more common now.

Anyways, if you need that kind of control, add watcher the open prop of your composition, and perform your custom side-effects there.