code: public HpackHeaderField remove() {
          HpackHeaderField removed = hpackHeaderFields[tail];
          if (removed == null) {
              return null;
          }
          size -= removed.size();
          hpackHeaderFields[tail++] = null;
          if (tail == hpackHeaderFields.length) {
              tail = 0;
          }
          return removed;
      }
docs: Remove and return the oldest header field from the dynamic table.