Here’s a tale of two cities for you: The villain is Mayor de Blasio, sentencing hundreds of minority, low-income schoolchildren to the educational guillotine.The mayor’s minions refuse to offer adequate space for new Success Academy middle schools. There’s ample room in buildings near the primary schools the children now attend, but the city Department of Education wants to make them travel long distances — forcing fifth-graders in Southeast Queens to tramp up to the South Bronx.