It’s a stretch of the Big Apple where laws don’t seem to exist. Squatters living in more than a dozen trailers and RVs — and even a decommissioned ambulance — have turned a Bronx street into a filthy nightmare, with illegal generators and propane tanks lining the sidewalk and waste from chemical toilets dumped right into the street. The unsightly scene has been an open secret for two years, according to locals. “They pump s–t out into the streets and then they don’t move, so the street sweepers