How to properly pass the unregister_nav_menu hook?

Question

With inspiration from this post and using the theme activation/deactivation hook hack by Krishna Sharma I'm trying to unregister a predefined nav_menu upon theme deactivation.

What is the proper way to use the unregister_nav_menu hook?

In summary here is what I'm doing now:

function onlyiol_deactivate() {
        global $_wp_registered_nav_menus;   
        $dappm_onlyiol = 'dappm_onlyiol';
        unregister_nav_menu( $dappm_onlyiol );
    }

The function below (taking from the inspiration post) adds the menu properly when the theme is activated but I cannot get it to remove the menu upon deactivation.

function onlyiol_activate() {
    if( function_exists( 'wp_nav_menu' ) ){
        register_nav_menu( 'dappm_onlyiol', 'Default BuddyPress Menu' );
        add_action( 'widgets_init', 'dappact_addmenu_onlyiol' );
    }
}
wp_register_theme_activation_hook('onlyiol', 'onlyiol_activate');

function onlyiol_deactivate() {
    global $_wp_registered_nav_menus;   
    $dappm_onlyiol = 'dappm_onlyiol';
    unregister_nav_menu( $dappm_onlyiol );
}
wp_register_theme_deactivation_hook('onlyiol', 'onlyiol_deactivate');


function dappact_addmenu_onlyiol(){
    $menuname = 'IOL Navigation Menu';
    $bpmenulocation = 'dappm_onlyiol';
    // Does the menu exist already?
    $menu_exists = wp_get_nav_menu_object( $menuname );

    // If it doesn't exist, let's create it.
    if( !$menu_exists){
        $menu_id = wp_create_nav_menu($menuname);

        // Set up default BuddyPress links and add them to the menu.
        wp_update_nav_menu_item($menu_id, 0, array(
            'menu-item-title' =>  __('Home'),
            'menu-item-classes' => 'home',
            'menu-item-url' => home_url( '/' ), 
            'menu-item-status' => 'publish'));

        wp_update_nav_menu_item($menu_id, 0, array(
            'menu-item-title' =>  __('Find Us'),
            'menu-item-classes' => 'findus',
            'menu-item-url' => home_url( '/findus/' ), 
            'menu-item-status' => 'publish'));

    } 
}

For convenience (and @Jan Fabry asked for this in this reference post) this is the activation/deactivation snippet. I am running this in a plugin.

/**
 * Provides activation/deactivation hook for wordpress theme.
 *
 * Usage:
 * ----------------------------------------------
 * Include this file before this line.
 * ----------------------------------------------
 * function my_theme_activate() {
 *    // code to execute on theme activation
 * }
 * wp_register_theme_activation_hook('mytheme', 'my_theme_activate');
 *
 * function my_theme_deactivate() {
 *    // code to execute on theme deactivation
 * }
 * wp_register_theme_deactivation_hook('mytheme', 'my_theme_deactivate');
 * ----------------------------------------------
 * 
 * @author Krishna Kant Sharma (http://www.krishnakantsharma.com)
 */

/**
 *
 * @desc registers a theme activation hook
 * @param string $code : Code of the theme. This can be the base folder of your theme. Eg if your theme is in folder 'mytheme' then code will be 'mytheme'
 * @param callback $function : Function to call when theme gets activated.
 */
function wp_register_theme_activation_hook($code, $function) {
    $optionKey="theme_is_activated_" . $code;
    if(!get_option($optionKey)) {
        call_user_func($function);
        update_option($optionKey , 1);
    }
}

/**
 * @desc registers deactivation hook
 * @param string $code : Code of the theme. This must match the value you provided in wp_register_theme_activation_hook function as $code
 * @param callback $function : Function to call when theme gets deactivated.
 */
function wp_register_theme_deactivation_hook($code, $function) {
    // store function in code specific global
    $GLOBALS["wp_register_theme_deactivation_hook_function" . $code]=$function;

    // create a runtime function which will delete the option set while activation of this theme and will call deactivation function provided in $function
    $fn=create_function('$theme', ' call_user_func($GLOBALS["wp_register_theme_deactivation_hook_function' . $code . '"]); delete_option("theme_is_activated_' . $code. '");');

    // add above created function to switch_theme action hook. This hook gets called when admin changes the theme.
    // Due to wordpress core implementation this hook can only be received by currently active theme (which is going to be deactivated as admin has chosen another one. 
    // Your theme can perceive this hook as a deactivation hook.)
    add_action("switch_theme", $fn);
}

According to A HitchHackers guide through WordPress this is the function that the unregister_nav_menu hook calls...

function unregister_nav_menu( $location ) {
    global $_wp_registered_nav_menus;
    if ( is_array( $_wp_registered_nav_menus ) && isset( $_wp_registered_nav_menus[$location] ) ) {
        unset( $_wp_registered_nav_menus[$location] );
        return true;  
    }
    return false;
}