update pkg/sftp to a stable version ...

... now that it contains all the needed patches.
Remove an hack for setstat with empty attrs, it is now handled in pkg/sftp.
Update other dependencies too.

sftpd/internal_test.go

@@ -299,12 +299,6 @@ func TestSetstatModeIgnore(t *testing.T) {
 	if err != nil {
 		t.Errorf("unexpected error: %v setstat should be silently ignore in mode 1", err)
 	}
-	setstatMode = 0
-	req := sftp.NewRequest("Setstat", "invalid")
-	err = connection.handleSFTPSetstat("invalid", req)
-	if err != sftp.ErrSSHFxBadMessage {
-		t.Errorf("unexpected error: %v", err)
-	}
 	setstatMode = originalMode
 }