Replacing star cornerback Chris Johnson, who was taken by Miami in the first round of the NFL Draft, is going to be one thing for the  San Diego State Aztecs . How about replacing the guys who accounted for 31 of the 32 sacks the Aztecs racked up as their defense set the tone for a 9-4 turnaround season?  That’s where the Aztecs find themselves heading into their first season in the new-look Pac-12.  There’s work to do in all three levels of SDSU’s defense, and it starts up front with the line, and particularly the EDGE rushers. Those are the guys who got things started for a defense that had an FBS-leading three shutouts. Who’s gone EDGES Trey White, Ryan Henderson and Niles King are all gone. White and Henderson, who tied for the team lead with seven, have moved on to bigger programs: White to Texas Tech for a reported $1.5 million and Henderson to Texas A&M.…