How to remove admin bar logo in WordPress using plugin

Question

I'm following the instructions from this page to remove the adminbar wordpress logo and cannot quite understand why this is not working in a plugin I have created.

// Hide top left WordPress logo

add_action( 'admin_bar_menu', 'remove_wp_logo', 999 );

function remove_wp_logo( $wp_admin_bar ) {
    $wp_admin_bar->remove_node( 'wp-logo' );
}

Everything else in my plugin is working except this. Only difference I see in that example is that it is referring to the functions.php file?

Any thoughts would be appreciated?