Working Demo http://jsfiddle.net/tUBxc/1
JS
$(document).ready(function () {
var text = $('.PageText_L329n')[0].nextSibling;
$(text).remove();
});
New Js by user2592238
$(document).ready(function () {
$("body:contains('Quantity in Stock')").each(function () {
var text = $(this).text();
text = text.replace("Quantity in Stock:", "");
$(this).text(text);
});
});