Always allow commenting a patch set

Prevent giving review scores but allow commenting for a change in
CI states (STAGING, STAGED or INTEGRATING). No need to block it with
error message like before. Also if the state has changed to one of
CI states while reviewing, review scores are dropped, just comments
are saved.

Task-number: QTQAINFRA-858
Change-Id: I684f004a1d680b2db184fedb50d936337f603721
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Ismo Haataja <ismo.haataja@digia.com>