By Marianna Parraga, Mayela Armas and Trevor Hunnicutt CARACAS/WASHINGTON (Reuters) -Some of the Americans who were freed by Venezuelan President Nicolas Maduro’s government in a U.S. prisoner swap have landed at a U.S. military base in San Antonio, Texas, a Reuters witness said. The individuals were freed on Wednesday in exchange for the U.S. release of an ally of Maduro, Colombian businessman Alex Saab, who was granted clemency by U.S. President Joe Biden and returned to Venezuela on Wednesday. Maduro also agreed to release at least 20 opposition-linked prisoners from prison. U.S. prosecutor…