Some of the world’s most influential institutions are selling shares of Asia’s technology giants after owning them for years, a troubling sign for investors after what has already been a painful market selloff. In recent months, Japan’s SoftBank Group Corp. has pared its stakes in the Chinese e-commerce company Alibaba Group Holding Ltd. and the Indian mobile-payments company Paytm, in both cases following declines in their share prices. Berkshire Hathaway Inc., Warren Buffett’s company, has been gradually reducing its stake in BYD Co., a Chinese electric-vehicle maker that it has owned shares in since 2008.