John Gambling City radio veteran John Gambling is out - and Curtis Sliwa is in.Gambling was fired from WABC, a victim of hard times at the station's parent company, Citadel Broadcasting.Sliwa will get Gambling's 10 a.m. slot starting Monday. Also out is WPLJ afternoon host Rocky Allen. Further changes seemed imminent following a scorched-earth fourth quarter financial report from Citadel CEO Farid Suleman. There was no official announcement from WABC or Citadel that Gambling and newsman George Weber were dismissed, but company sources confirmed it. They said Sliwa will take over Gambling's 10-11:45 a.m. slot. That's a prominent position...