Why is Donald Trump hosting “Saturday Night Live†next weekend after NBC canceled the Miss Universe pageant? “It’s called ratings,†Trump told The Post. “I go on Jimmy Fallon, he got his best ratings. One of the best nights he’s had in years. Then I did Colbert’s show. That got fantastic ratings. He beat Fallon by a lot. Since then, NBC and I get along great.†“The Tonight Show†drew 4.46 million viewers when Trump appeared on Sept. 11, its biggest Friday audience in 18 months. Trump’s Sept. 22 sit-down on “The Late Show†on CBS averaged 4.56 million viewers,...