Removes a vertex from the linked list
function(vertex) {
      if (vertex.prev === null) {
        this.head = vertex.next;
      } else {
        vertex.prev.next = vertex.next;
      }

      if (vertex.next === null) {
        this.tail = vertex.prev;
      } else {
        vertex.next.prev = vertex.prev;
      }

      return this;
    }