In homes and pubs, on leaflets and lampposts, debate is raging in Ireland over whether to lift the country’s decades-old ban on abortion. Pro-repeal banners declare: “Her choice: vote yes.” Anti-abortion placards warn against a “license to kill.” Online, the argument is just as charged — and more shadowy, as unregulated ads of uncertain origin battle to sway voters before Friday’s referendum, which could give Irish women the right to end their pregnancies for the first time. The highly charged campaign took a twist this month when Facebook and Google moved to restrict or remove ads relating to the abortion vote.