delete unused code

middleware/auth/session_redis.go

 
 import (
 	"github.com/go-redis/redis"
-	"sync"
 	"time"
 )
 
-type RedisSessionStore struct {
-	once   *sync.Once
-	client *redis.Client
-}
+type RedisSessionStore struct{ client *redis.Client }
 
 func NewRedisSessionStore(address string, password string) *RedisSessionStore {
-	session := &RedisSessionStore{once: &sync.Once{}}
+	session := &RedisSessionStore{}
 	session.client = redis.NewClient(&redis.Options{
 		Addr:     address,
 		Password: password,