By Jason Buch, Evan Garcia and Ted Hesson SAN ANTONIO (Reuters) -The death toll from a human trafficking incident on Monday in which migrants suffered under extreme Texas heat inside a truck rose to 50, U.S. and Mexican officials said on Tuesday, in one of the most fatal incidents of human smuggling along the U.S.-Mexico border in recent history. The migrants died inside a tractor-trailer in San Antonio, Texas, where temperatures swelled to a high of 103 degrees Fahrenheit (39.4 degrees Celsius). Local authorities responded on Monday afternoon to a remote area in the city’s southern outskirts …