Mikaela Shiffrin had nothing left to prove. Yet, standing in the Olympic slalom start gate last February, the GOAT of skiing didn’t feel like she was playing with house money. “Even though it is just a ski race, it is also not just a ski race,” she said during a revealing 25-minute conversation at Copper Mountain last Saturday. Shiffrin introspectively analyzed last season and looked ahead to what’s next. With 110 World Cup wins to her name, it’…