By Crispian Balmer BEIRUT (Reuters) - Austria said on Thursday it would pull out of a U.N. force on the Golan Heights after battles between Syrian troops and rebels there, in a blow to a mission that has kept the Israeli-Syrian war front quiet for 40 years. Israel, anxious for the international mission to remain in place, worried that the Golan could become a springboard for attacks on Israelis by Islamist militants fighting to oust Syrian President Bashar al-Assad. ...