The FDNY on Monday moved to curb soaring medical leave among firefighters by reducing staffing on engine companies. Effective on Tuesday at 9 a.m., the FDNY will no longer assign a fifth firefighter to the 10 engine companies that had carried an extra set of hands, the Daily News has learned. The absenteeism rate includes time taken off to recover from injuries as well as sick days to recuperate from an illness. The Uniformed Firefighters’ Association that represents the city’s roughly 8,000 rank-and-file Bravest issued a memo alerting all members to the change — and it included a pointed reminder that the fifth firefighter will only return if sick leave drops next month.