Script for using .remove() when there are two forms being used on the page (one for desktop, one for mobile)
var MobileForm = $('.side-content--mobile');
var DesktopForm = $('.side-content--desktop');
MobileForm.find('#item_id option:not(:selected, [value="3491"],[value="3492"])').remove();
DesktopForm.find('#item_id option:not(:selected, [value="3491"],[value="3492"])').remove();