Sorry, typo in the trigger code.
it should be:
if (isset($_GET["clear"])) {
If you where to crate a new php page and add the eCart Display Manager to it and use the Quick Cart display type, the use framework builder to include that page a s a plugin to show the cart quantity and price, you could do the same modification to create another instance of the clear cart behavior using the clear URL variable.
the way you are using bare HTML pages as php includes wont work for this though.