Remove form onSuccess
HTML
<script src="//app-sj01.marketo.com/js/forms2/js/forms2.min.js"></script>
<form id="mktoForm_96"></form>
<script>MktoForms2.loadForm("//app-sj01.marketo.com", "410-XOR-673", 96,
function(form) {
form.onSuccess(function(form){
formElem = this.formElem[0];
formParent = formElem.parentNode;
formParent.removeChild(formElem);
formParent.innerHTML = 'All gone!';
});
});
</script>