Messages relay fixes (#2073)

* removed obsolete check that is superseded by the unblock checks below

* if messages race transaction submit has failed, do not restart loop. Instead, wait for new best nonces from target node and retry selection. That's because submit has probably failed because other relayer has submitted same nonces

* reset nonces_to_submit and nonces_submitted if at least one of selected/submitted nonces is already at target

* removed extra check