I killed Grandma with a fake elephant tusk! That’s what a deranged Hamilton Heights man told cops, according to a bizarre confession made public yesterday. Dominick Anderson grabbed the weapon after he became convinced his grandmother had put a voodoo curse on him, he allegedly told cops after the Dec. 19 murder in his family’s apartment. “I killed my grandmother with a cream-colored elephant tusk, and I did it because she was trying to have me killed,” Anderson, 26, said of the attack, which left the tusk in pieces, the grandmother, Beverly Holmes, 62, dead and Anderson’s sister injured. . .