code: private HeaderField remove() {
      if (size == 0) {
        return null;
      }
      HeaderEntry eldest = head.after;
      int h = eldest.hash;
      int i = index(h);
      HeaderEntry prev = headerFields[i];
      HeaderEntry e = prev;
      while (e != null) {
        HeaderEntry next = e.next;
        if (e == eldest) {
          if (prev == eldest) {
            headerFields[i] = next;
          } else {
            prev.next = next;
          }
          eldest.remove();
          size -= eldest.size();
          return eldest;
        }
        prev = e;
        e = next;
      }
      return null;
    }
docs: Remove and return the oldest header field from the dynamic table.