Remove warning, when dropping top- on top-node
Remove warning, when dropping top- on top-node

Close #369

dewhisna/fancytree,spilmert/fancytree,grandmanitou/fancytree,Koloto/fancytree,spilmert/fancytree,hglty07/fancytree,HobieCat/fancytree,Aliccer/fancytree,dewhisna/fancytree,jiangjunt/fancytree,hglty07/fancytree,hglty07/fancytree,jiangjunt/fancytree,HobieCat/fancytree,grandmanitou/fancytree,spilmert/fancytree,Aliccer/fancytree,HobieCat/fancytree,Mats0/fancytree,Koloto/fancytree,dewhisna/fancytree,jiangjunt/fancytree,Mats0/fancytree,grandmanitou/fancytree,Aliccer/fancytree,Koloto/fancytree