The world’s two most populous nations will try to remove a long-term irritant in their relations by signing a border agreement. The Border Defense Cooperation Agreement may be signed during Indian Prime Minister Manmohan Singh’s visit to China, which starts on Tuesday, Press Trust of India said. The deal, along with Singh’s visit, is a sign of improved Sino-Indian ties, experts said. Premier Li Keqiang visited India in May. In a statement before departing on his five-day trip to Russia and…