src/event/EventManager.php
public function detach(\SplObserver $observer) {
        foreach ($this->_observers as $observerItem) {
            if ($observerItem->observer === $observer) {
                $this->_observers->detach($observerItem);
            }
        }
    }
public function detach(\SplObserver $observer) {
        foreach ($this->_observers as $observerItem) {
            if ($observerItem->observer === $observer) {
                $this->_observers->detach($observerItem);
            }
        }
    }
Delete the observer from the list

@param \SplObserver $observer