By Michelle Nichols UNITED NATIONS (Reuters) – The United Nations General Assembly on Thursday agreed on a definition of denial of the Holocaust, when the Nazis killed 6 million Jews during World War Two, and urged social media companies “to take active measures” to combat antisemitism. “The General Assembly is sending a strong and unambiguous message against the denial or the distortion of these historical facts,” said Germany’s U.N. Ambassador Antje Leendertse. “Ignoring historical facts increases the risk that they will be repeated.” While the 193-member General Assembly adopted the resolution – drafted by Israel and Germany – without a...