ui.widget: Improves Performance of cleanData-Method. Fix for http://bugs.jqueryui.com/ticket/9546

The cleanData-Method triggered "remove" on all elements in the tree.
After the fix the remove-handler will only be triggered if there is at least
one event bound to the element. Doing so increases performance significantly.
performance-comparison http://jsfiddle.net/felvhage/r7buw/

Fixes #9546