Barge boards per se were not outlawed. What they (the FIA) did was create non-aero zones around the car where aero devices were not permitted, the key one of these being in the region where barge boards had been sited previously. What some teams, notably Ferrari and RBR have done is move the sidepods rearwards, allowing some room between them and the non-aero zone for an aero device cunningly disguised as a mirror mount.
It's a bone of contention at the moment with some teams saying that whilst it is not against the letter of the rule, it is against the spirit of the rule. What they tried to do with the non-aero zones is to reduce the turbulence coming off the car so that cars following would not be robbed of downforce ergo grip. What these new "mirror mounts" do is tidy the air up before it goes around the rear wheels and in doing so create turbulence behind the car.