code: def delete(self, key):
          
          del self._cache[key]
          self._order.delete(key)
          self._size -= 1
docs: >>> c = LRUCache()
          >>> c.put(1, 'one')
          >>> c.get(1)
          'one'
          >>> c.delete(1)
          >>> c.get(1)
          Traceback (most recent call last):
              ...
          KeyError: 1
          >>> c.delete(1)
          Traceback (most recent call last):
              ...
          KeyError: 1