Eddie Murphy was slated to do a Bill Cosby impression during “Saturday Night Live’s” 40th-anniversary show, but turned down the gig at the last minute so as not to “kick” the embattled comedian “when he was down,” another former “SNL” member revealed Wednesday. Murphy was expected to play Cosby during a “Celebrity Jeopardy!” skit with the category “Potent Potables” alluding to allegations Cosby spiked women’s drinks and raped them, Norm Macdonald tweeted. But Sunday, the day of the show, Murphy backed out. “He knew the laughs would bring the house down. Eddie Murphy knows what will work on ‘SNL’ better...