remove(index) {
        const brk = this._node.children[index];
        if (brk) {
            this._node.children.splice(index, 1);
            this._node.attributes.count--;
            if (brk.man) {
                this._node.attributes.manualBreakCount--;
            }
        }

        return this;
    }
remove page-breaks by index
@param {number} index - index of list
@return {PageBreaks} the page-breaks