Remove call to Element#undrag from hideHandles

In my app I'd like to show handles on active elements. Clicking or draging an element should activate the element. Because ``hideHandles`` removes drag events, that isn't really possible. This patch removes the call to ``Element#undrag``.

I realise that this may break someone else's application. An alternative to just removing this code would be to make it possible to disable that call by some kind of default parameter.

Cheers,
Miloš