unbind escape handler after closeVbox() is called
unbind escape handler after closeVbox() is called

An escape key handler is bound to the keydown event of the body,
which in turn calls closeVbox() to dismiss the lightbox.

This commit ensures the escape handler is unbound when closeVbox()
is called, because it's no longer needed.

nicolafranchini/VenoBox,postyou/VenoBox,Kubik-Rubik/VenoBox