prova cosi:
codice:
function delete() {
  var children = document.getElementById('subsections').childNodes.length;
var opt = document.getElementById('subsections')
  while(children>0) {
    opt.removeChild(opt.lastChild);
    children--;	
  }
  return 0;
}
oppure cosi:
codice:
function delete() {
  var children = document.getElementById('subsections').childNodes.length;
var opt = document.getElementById('subsections')
  while(children>0) {
    opt.options.remove(opt.options.length-1);
    children--;	
  }
  return 0;
}