By Michael Holden and Elizabeth Piper LONDON (Reuters) -Former finance minister Rishi Sunak won the biggest backing from Conservative lawmakers on Wednesday in the first vote to choose who will succeed Boris Johnson as party leader and British prime minister, while two more rivals were eliminated. Sunak, whose resignation as finance minister last week helped precipitate Johnson’s fall, secured support from 88 of the party’s 358 Members of Parliament (MPs), with junior trade minister Penny Mordaunt second with 67 votes and foreign minister Liz Truss third with 50. Nadhim Zahawi, who took over a…