gistfile1.js

/**
 * reset all the radio buttons with a given name
 *
 * @param string fieldName
 * @param object form
 * @return null
 */
function unselectRadio(fieldName, form)
{
  for( i=0; i < document.forms[form].elements.length; i++) {
    if (document.forms[form].elements[i].name == fieldName) {
      document.forms[form].elements[i].checked = false;
    }
  }
  return;
}

gistfile2.html

<a onclick="unselectRadio('gender', 'Main');return false;" title="unselect" href="#">unselect</a>

from js/Common.js in CiviCRM 3.1.5.