cleanup() {
    if (this.sectionStart !== this.index) {
      if (this.state === 1 || this.state === 32 && this.sequenceIndex === 0) {
        this.cbs.ontext(this.sectionStart, this.index);
        this.sectionStart = this.index;
      } else if (this.state === 19 || this.state === 20 || this.state === 21) {
        this.cbs.onattribdata(this.sectionStart, this.index);
        this.sectionStart = this.index;
      }
    }
  }
Remove data that has already been consumed from the buffer.