The reason why the vertical scroll bar is always visible is because it makes width calculations more reliable as the height of the browser content changes. This means that when content grows to require a scrollbar to appear, the reduction in horizontal space (to accommodate the appearance of a scrollbar) will not result in elements that were sized to fit the previously available width will not flow unexpectedly.
You should be able to disable the rule (as long as you're referring to the selector targeting the html element). I've just tried this using browser developer tools in Chrome and see that the scrollbar does indeed get removed.
However, I would urge caution in doing this because you may find that doing so results in further undesirable behaviour that you then need to fix. Unless you have a really valid reason (i.e. not a purely cosmetic reason) then I would recommend leaving the default as it is.