Fat, weak and slow is no way to become a cop — or is it? The NYPD dramatically relaxed the fitness requirements to become a city cop amid a record wave of retirements that has the brass desperate for warm bodies to fill the ranks, The Post has learned The department replaced a faux 6-foot wall inside the Police Academy gym with a chain-link fence that’s easier to climb, according to official recruiting videos posted online. The move came after a cellphone was used last year to record a series of out-of-shape, wannabe cops laughably trying — and failing —...