Det. Munch retiring after 20 years in prime time: After 21 years as a cop, spanning seven seasons on “Homicide: Life on the Street” and 14 seasons on “Law & Order: Special Victims Unit” — plus guest appearances on series ranging from “The Wire” to “Arrested Development” — Richard Belzer’s conspiracy-prone cop is hanging up his SVU badge on Wednesday’s episode (9 p.m./Ch. 4). So long, John. Thanks to you the entire world of fictional TV took place in the mind of an autistic child.