ATLANTA — A federal judge struck down a section of a Georgia law on Wednesday that would have made it a crime to knowingly harbor or transport an illegal immigrant while committing another crime, from speeding to more serious violations. U.S. District Court Judge Thomas Thrash issued an order to scrap that section of the law, saying that a federal appeals court has already found it to be pre-empted by federal law. He also ordered the state to inform several state agencies that would have been involved in enforcing that provision of his decision.