MEXICO CITY (Reuters) -Mexico’s government on Saturday moved to discourage the formation of caravans by Venezuelan migrants, saying any who do will not be eligible to enter the United States under a new humanitarian scheme announced this week. Under a plan announced on Wednesday, Washington said it would grant up to 24,000 Venezuelans humanitarian access to the United States by air, while enabling U.S. officials to expel to Mexico those caught trying to cross illegally by land. The plan is the latest bid to curb record numbers of illegal crossings at the Mexico-U.S. border fueled in part by a …