I think that tapir interface went away in UC2, I have made this workaround for my project, in a custom module:
<?php
function mymodule_form_alter(&$form, $form_state, $form_id) {
if ($form_id == 'uc_cart_view_form') {
//This line disables qty column
unset($form['items']['#columns']['qty']);
//This loop denies access to all qty fields for the form
foreach($form['items'] as &$item) {
if (is_array($item) & isset($item['qty'])) {
$item['qty']['#access'] = 0;
}
}
}
}
?>