The lionized former principal of a Dyker Heights school — whose 50-year tenure made her the longest serving principal in New York City history — died on April 9 at the age of 93.  Madeleine Brennan took the helm of Dyker Heights Intermediate School 201 on 1963 after working as a teacher in the New York City school system for 17 years. Her leadership and compassion made her a beloved fixture of the school and the surrounding community until her retirement in 2013, educators said.  “She’s an icon, a remarkable woman,” said Robert Ciulla, the current principal of Dyker Heights I.S. 201, who worked with Brennan for more than…