If you want to use the iframe’s scrollbar and not the parent’s use this:
document.body.style.overflow = 'hidden';
If you want to use the parent’s scrollbar and not the iframe’s then you need to use:
document.getElementById('your_iframes_id').scrolling = 'no';
or set the scrolling="no"
attribute in your iframe’s tag: <iframe src="https://stackoverflow.com/questions/2469529/some_url" scrolling="no">
.