A Latin American mobile app that Cambridge Analytica had hoped to use to mine data for Mexican presidential campaigns has severed ties with the embattled political-advertising firm after the Facebook Inc. data scandal erupted. Pig.gi, which gives 1.2 million users in Mexico and Colombia free airtime and data in exchange for watching ads and taking surveys, says it’s never worked on a political campaign with Cambridge. The startup did share results on two election polls and occasional aggrega...