[#1] Update comment lines

Signed-off-by: Alex Vanin <a.vanin@yadro.com>

internal/frostfs/services/tree_client_grpc_signature.go

@@ -7,8 +7,6 @@ import (
 )
 
 func (c *ServiceClientGRPC) signData(buf []byte, f func(key, sign []byte)) error {
-	// crypto package should not be used outside of API libraries (see neofs-node#491).
-	// For now tree service does not include into SDK Client nor SDK Pool, so there is no choice.
 	// When SDK library adopts Tree service client, this should be dropped.
 	sign, err := crypto.Sign(&c.key.PrivateKey, buf)
 	if err != nil {