Original text: He remembered N____r Island as a boy. . . . It had got its name from its resemblance to a man's head--a man with negroid lips.
Revised text: He remembered Indian Island as a boy. . . . It had got its name from its resemblance to a man's head--an American Indian profile.
(Source: Sanders and Lovallo, The Agatha Christie Companion [New York: Delacorte Press, 1984], 182)
Interestingly, in the last few years the term "Indian" referring to the indigenous peoples of North America has, in turn, become offensive to some groups. "Native American" is usually the preferred term nowadays. This has resulted in yet another change to the novel--removal of the references to "Indian Island" and "Ten Little Indians" and insertion of "Soldier Island" and "Ten Little Soldiers." It's difficult to imagine that the term "soldier" will ever become offensive.
For a thoughtful discussion of the term "Indian," see this usage note.