Remove round in the same transaction as getting it

[Kukunin]

It avoid race condition when multiple blockUnlockers instances are running, and they add the reward multiple times.

Before this, two instances might both have taken the same round information, remove it and adds the same reward twice, which ruins the statistic.

[Kukunin]

This code isn't tested, as there is no automatic tests suit and also I don't know the best way to test it.

Please review and give me your opinion on it