A convicted sex offender who allegedly cold-cocked a man on a Bronx street — leaving him in a coma with brain injuries — was freed without bail Thursday after getting his attempted-murder charges reduced in the unprovoked attack. Bui Van Phu, 55, was instead charged by the Bronx District Attorney’s Office with assault and harassment, both misdemeanors, for the brutal knockout punch last Friday that left 52-year-old Jesus Cortes unconscious on the street ... The NYPD had charged Phu with attempted murder after arresting him Wednesday for the attack that appeared to have come out of the blue. .... Phu...