NEW YORK — Twenty years after a ringing fire bell and a solemn ceremony marked the end of the hellish cleanup effort at ground zero, Gov. Kathy Hochul said Monday that a hole remains in New York’s heart despite the grand redevelopment of the area where the twin towers once rose. “We will never forget this. Never, ever,” Hochul said of the Sept. 11 attack. “For many, the devastation, the loss occurred on that day: 9/11. But there’s so many who know the bigger story. For 260 days, people showed up here exposed to toxins and contaminants.” The cleanup was more than merely the removal of nearly 2 …