JERUSALEM, July 16 (Reuters) - Israeli Prime Minister Benjamin Netanyahu ordered the ejection on Sunday of an activist from his Likud party who mocked the Holocaust while heckling anti-government protesters, in remarks that suggested ethnic tensions beneath a constitutional crisis. Video circulated on social media showed Itzik Zarka cursing and spitting at demonstrators at a traffic junction near the working-class town of Beit Shean on Saturday. "It's not for nothing that six million were killed," he shouts. "I'm proud that six million of you were burned!" "We will not tolerate such disgraceful behaviour in the Likud movement," Netanyahu said in...