Hi,
Using the jomla menu/module system it's a bit tricky... You should create a menu linking to the checkout. Then, in the cart module joomla options, restrict the module display to the pages where you need it excluding the checkout page. and then modify the file cart of the view product to force the itemid in the action of the form so that it goes to the checkout itemid page. Not so easy...
Otherwise, you could edit the file cart of the view product in the HikaShop menu "Display->Views" and add a check like this :
if(JRequest::getVar('option','')=='com_hikashop' && JRequest::getVar('ctrl')=='checkout'){
// display nothing on the checkout
}else{
// display the normal cart page
}