HARARE (Reuters) - Zimbabwe s former vice president Emmerson Mnangagwa, who was sacked by President Robert Mugabe this week, has been expelled from the ruling Zanu-PF, a party spokesman said on Wednesday. Mnangagwa, a liberation war veteran and a long-time ally of Mugabe, was until this week seen as a favorite to succeed the 93-year-old leader. But Mnangagwa s relationship with Mugabe s wife, Grace, has become increasingly strained as their two factions within Zanu-PF fight for dominance. Mnangagwa s removal on Monday came two days after Grace publicly called him a  coup plotter . 