Dennis Richmond’s retirement announcement yesterday offered no clues about who will replace him on the market’s top-rated newscast. “Mornings on 2” co-anchor Frank Somerville had been seen as the heir apparent until last October, when Channel 2 hired Dave Clark (pictured), who had been an anchor for KCBS-KCAL in Los Angeles. In an e-mail to friends (which was obtained by LA Observed and Matier & Ross) Clark suggested he was being groomed as a replacement for Richmond. Clark started at Channel 2 on Nov. 1 doing the early morning news, replacing Mark Curtis. Curtis is now a reporter at Channel 2. At the time, management denied Clark was in line to replace Richmond.