Method remove

code/chapter09/lru.rs:67–72

(&mut self, key: &K)

    }

    fn remove(&mut self, key: &K) -> Option<V> {
        self.map.remove(&key).map(|index| {
                self.remove_from_list(index);
                self.entries[index].val.take().unwrap()
            })
    }

    fn get(&mut self, key: &K) -> Option<&V> {
        if self.contains(key) { self.access(key); }