Maserati last summer launched a track-only version of its MC20 supercar in the form of the MCXtrema, but it isn’t the first time the automaker has treaded down such a path. Back in 2006, Maserati took the covers off the MC12 Versione Corse, a track-only version of the V-12-powered MC12 supercar. Just 12 were built, plus a prototype, and now one of…