Add extra class to Revolution Slider element in visual composer, example “nomargin”
After add custom CSS for this class in page setting (icon gear in top right)
.nomargin {margin-bottom: 0 !important }
it will remove white 35px gap after revolution slider on page
If you need remove gap from all sliders on your site, you must put extra class for each and put custom css rule in Dashboard: Theme Options -> Custom CSS/JS : CSS field