you can find the number of items where RecID = 6 using conditional total:
<?php echo $eCart1->ConditionalTotal("Quantity", "RecID", "6"); ?>
so you could set the if statement to hide the delete button as:
if($eCart1->ConditionalTotal("Quantity", "RecID", "6") > 1) {
in other words,
If the quantity of items in the cart where the RecID column has a value of 6 is Greater than 1...