creds/s3: remove unused package

Signed-off-by: Roman Khimov <roman@nspcc.ru>

creds/s3/secret.go

@@ -1,19 +0,0 @@
-package s3
-
-import (
-	"crypto/sha256"
-	"encoding/hex"
-
-	"github.com/nspcc-dev/neofs-api-go/pkg/token"
-)
-
-// SecretAccessKey returns secret access key generated by BearerToken.
-func SecretAccessKey(tkn *token.BearerToken) (string, error) {
-	data, err := tkn.Marshal()
-	if err != nil {
-		return "", err
-	}
-
-	hash := sha256.Sum256(data)
-	return hex.EncodeToString(hash[:]), nil
-}