remove unused packet cases from request.update

fstat and fsetstat are not converted to versions that work on path
instead of working with open filehandle. So I removed them from the
request.update method which updates the request object for methods that
are working on an opened file.
diff --git a/request.go b/request.go
index f21aca8..cd79e48 100644
--- a/request.go
+++ b/request.go
@@ -270,11 +270,6 @@
 		pd.offset = int64(p.Offset)
 	case *sshFxpReaddirPacket:
 		r.Method = "List"
-	case *sshFxpFsetstatPacket:
-		r.Method = "Setstat"
-		r.Attrs = p.Attrs.([]byte)
-	case *sshFxpFstatPacket:
-		r.Method = "Stat"
 	default:
 		return errors.Errorf("unexpected packet type %T", p)
 	}