'Mouse event processor which removes the top artist
under the cursor.  Connect this to the \'mouse_press_event\'
using::
canvas.mpl_connect(\'mouse_press_event\',canvas.onRemove)'

def onRemove(self, ev):

    under = sorted(self.figure.hitlist(ev), key=(lambda x: x.zorder))
    h = None
    if under:
        h = under[(-1)]
    while h:
        if h.remove():
            self.draw_idle()
            break
        parent = None
        for p in under:
            if (h in p.get_children()):
                parent = p
                break
        h = parent
