Honestly, looking at some of the pictures it kind of looked like they did remove them. When they put the Vikings turf on, when the turf was mostly installed you could clearly see the coils under the remaining portion. When they put this turf on you could not see them. Now, it could just be that the coils settled into the sand that is under the carpet and they aren't visible. Or they added sand on top, whatever.
I wouldn't be surprised either way. I know that there is maintenance and you do need to periodically run them just to keep the system in good shape and all that costs money. But how much money and whether it is enough to justify removing (which also costs money), that I'm not sure.
Frankly, it's kind of a non-issue. There's been one Gopher game I can think of where the heated field would have been a significant benefit (if I remember right Iowa in 2010. Though you could argue the frozen field evened the teams enough to allow the Gophers to win). And if there's ever a fluid leak under the field you'll never hear the end of it - the U will probably demolish the stadium and turn it into a park to appease the environmentalists.