Try something like this after your code in the change event of the drop down
for (var i = 0; i < this.items.nodes.length; i++ )
{
sValue = this.resolveNode("items.#text[" + i + "]").value;
if ( sValue === xfa.event.newText )
{
this.deleteItem( i );
xfa.event.change = "";
break;
}
}