Britney Spears’ new attorney, Mathew Rosengart, has declared he’s working “aggressively and expeditiously” to have the singer’s father, Jamie Spears, removed as her conservator.Rosengart – a former federal prosecutor who’d previously worked with Sean Penn and Steven Spielberg – was appointed Spears’ lawyer last week, after a judge granted the singer permission to appoint her own legal representation in the legal battle over her conservatorship.Following a brief hearing in the Los Angeles