Method unregister

src/aria/private/utils/collection.ts:38–44

(item: T)

  }

  unregister(item: T) {
    this._items.update(set => {
      const newSet = new Set(set);
      newSet.delete(item);
      return newSet;
    });
  }

  startObserving(element: HTMLElement) {
    if (this._observer) {