Sometimes it's just simpler to use the native API when working with next nodes.
var select = $("div > select")[0];
select.parentNode.removeChild(select.previousSibling);
You can also make your selector a little more specific if need be.
var select = $("div > input + select")[0];
You could use jQuery to do the remove as well if you did this:
var select = $("div > input + select")[0];
$(select.previousSibling).remove();
which means you could do it in one line:
$($("div > input + select")[0].previousSibling).remove();
but that gets a little hard to read.