Racist, homophobic and ethnic slurs used by comedian Shane Gillis have resurfaced online in the wake of the news he’ll be hosting “Saturday Night Live” — the show that once fired him due to his past problematic behavior. ‘SNL’ on Saturday announced Gillis as the host of its Feb. 24 episode, alongside musical guest 21 Savage. But it didn’t take long for pushback on the casting decision, with many recalling the controversial jokes and offensive language he previously used on his podcasts. In clips from the show “A Fair One,” gathered by TMZ on Tuesday, Gillis can be heard using the n-word, as we…