Remove person from `kickedOnceList` when he is ban.

When someone is kicked from flood, he is added to kickedOnceList so
that the bot may :
  - know that it should ban him next time
  - ignore his queries (to avoid command spam)
However, when someone is banned and then unbanned, he has to be removed
from kickedOnceList so that he may have access to normal commands in
query (!cards, pl xx, bid xx xx, ...).