Fix gometalint errors

Signed-off-by: Manish Tomar <manish.tomar@docker.com>

registry/storage/driver/s3-aws/s3_v2_signer.go

@@ -39,12 +39,6 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-const (
-	signatureVersion = "2"
-	signatureMethod  = "HmacSHA1"
-	timeFormat       = "2006-01-02T15:04:05Z"
-)
-
 type signer struct {
 	// Values that must be populated from the request
 	Request      *http.Request