A maniac repeat offender released from a psych ward after just an hour allegedly shoved an elderly man to his death down Manhattan subway steps in an unprovoked attack Thursday night — with an outraged poilce source blasting the killing as a “complete collapse” of City Hall’s approach to mental health. Rhamell Burke — a 32-year-old serial troublemaker who has been arrested four times since February — mysteriously walked free from Bellevue Hospital about an hour after cops cuffed him and checked him in as an “emotionally disturbed person” around 3:30 p.m. Thursday, according to police. The violent brute was...