How to alter Nodereference_url

I'd like to alter Nodereference url widget by my own condition,
so first i need to unset Nodereference url links.

i tried to use my custom module,

function mymodule_node_view($node, $view_mode, $langcode) {
    if ($nodereflinks = nodereference_url_build_all_links($node, $view_mode)) {
        unset($nodereflinks);
    }	
}

or

function mymodule_node_view_alter(&$build) {
  // Remove the read more link
  unset($build['links']['node']['#links']['signup_field_event_signup']); //my nodereff field
  unset($build['links']['node']['#links']['signup-field-event-signup']); //my nodereff field
}

doesn't work.
Thank in advance