Rae Sremmurd leads the Billboard Hot 100 (dated Dec. 31) for a sixth week with "Black Beatles," featuring Gucci Mane. Meanwhile, Zayn and Taylor Swift's "I Don't Wanna Live Forever (Fifty Shades Darker)" debuts at No. 6, marking Swift's 20th Hot 100 top 10, and J. Cole's "Deja Vu" begins at No. 7. …