By Gram Slattery, Nathan Layne and James Oliphant FRANKLIN, N.H. (Reuters) -Donald Trump’s last remaining Republican opponent, former U.N. Ambassador Nikki Haley, was making a final push on Monday to convince New Hampshire voters to turn out and deliver her an upset victory in the state’s presidential nominating contest. New Hampshire’s primary vote on Tuesday will split the state’s Republican voters into two camps: those with former President Trump, and those against him. The contest became a one-on-one race on Sunday, when Florida Governor Ron DeSantis ended his struggling campaign and endor…