You want Wit's End because of your passive so you don't want to remove the Attack Speed it gives you, and with Nashor's Tooth you lose the Magic Resistance.

i removed wit´s end too, but i´ve got add a nashor´s tooth instead of it, it is more usefull

I have seen a couple of shyv's replace their wit's end with a Warmogs and it works very well if you have a FM and a Atma's