menu_tree_output() not returning full menu array
From what I understand about menu_tree_all_data() you need to supply it a link and depth to give it context (where in the menu tree am I at &amp; how far do I go?). Also drupal_render() expects an argument passed by reference, so there will problems passing the output of function.

// Default to root link w/ a depth 5.
$link = menu_get_item();
$tree = menu_tree_all_data("devel-frus", $link, 5);
$tree_output = menu_tree_output($tree);

// Supply a variable for drupal_render to reference.
$menu = drupal_render($tree_output);

$nocss = preg_replace('/class=".*?"/', '', $menu);
echo($nocss);