Dialog demo: Remove a duplicate (and incorrect) script include

Author: tjvantoll

demos/dialog/modal-message.html

@@ -12,7 +12,6 @@
 	<script src="../../ui/draggable.js"></script>
 	<script src="../../ui/position.js"></script>
 	<script src="../../ui/resizable.js"></script>
-	<script src="../../ui/jquery.ui.button.js"></script>
 	<script src="../../ui/dialog.js"></script>
 	<link rel="stylesheet" href="../demos.css">
 	<script>