Spencer Rattler ain’t walking through that door. Nor is Xavier Legette, for that matter. While the South Carolina defense returns most of its difference-makers from a season ago, it’s an offseason of change on the offensive side where the Gamecocks will debut new personnel at key positions — and potentially employ a new-look scheme as well. “Ever since that last game, that’s what you processed,” South Carolina offensive coordinator Dowell Loggains said in a pre-spring interview. “Like, you’re just sitting there saying, how do we replace (No.) 7 (Rattler)? How do we replace 17 (Legette)? How do…