Refactor list_reset_parent using cll#_iter

[make-github-pseudonymous-again]

Need to implement #17 first to check for performance. See also make-github-pseudonymous-again/js-library#7 (comment).

import { _iter } from '@aureooms/js-cll';
export default function list_reset_parent(children) {
        for ( const x of _iter(children) ) x.parent = null ;
}