Sema: Remove a bit of dead code

Author: slavapestov

lib/Sema/TypeCheckAvailability.cpp

@@ -2394,11 +2394,6 @@ class AvailabilityWalker : public ASTWalker {
     FragileKind = DC->getFragileFunctionKind();
   }
 
-  // FIXME: Remove this
-  bool shouldWalkAccessorsTheOldWay() override {
-    return true;
-  }
-
   bool shouldWalkIntoSeparatelyCheckedClosure(ClosureExpr *expr) override {
     return false;
   }