StackSize porting mod error 1.12.2

[richie995]

I'm porting mob properties from 1.10.2 to 1.12.2 in eclipse and I've received the following error 

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private int removeDrop(final Item item, final int damage, int count, final boolean infinite, final List<EntityItem> drops) {
        final Iterator<EntityItem> iterator = drops.iterator();
        while (iterator.hasNext()) {
            final EntityItem drop = iterator.next();
            final ItemStack dropStack = drop.getItem();
            if (item == dropStack.getItem() && (damage < 0 || damage == dropStack.getItemDamage())) {
                if (infinite) {
                    iterator.remove();
                }
                else {
                    count += dropStack.stackSize;
                    if (count < 0) {
                        iterator.remove();
                    }
                    else {
                        if (count == 0) {
                            iterator.remove();
                            return 0;
                        }
                        dropStack.stackSize = count;
                        drop.setEntityItemStack(dropStack);
                        return 0;

I'm relatively new to porting mod, so I'm unsure of what to do. The bolded functions are ones highlighted in red in eclipse. For the error "setEntityItemStack" when hovered over it says "The method setEntityItemStack(ItemStack) is undefined for the type EntityItem" and when hovering over "stacksize" it says "The field ItemStack.stackSize is not visible" I'm unsure of how to fix this error, and could use some help