I just installed your and got error (title), so I looked at the code and found its a valid function but it doesn't load every, so in order to make it work you need to make it like
require_once( ABSPATH . '/wp-admin/includes/plugin.php' );
// Makes sure the plugin is defined before trying to use it
if (is_multisite() && is_plugin_active_for_network(plugin_basename(FILE)))
add_action('admin_bar_menu', array($this, 'remove_network_comment_items'), 500);
I tried to send merge request but I dont' know how to send the pull request :(, been learning recenlty but no luck yet.
Oh yes, very often I had this problem and here I had it forgotton.
I will fix this now.
Thanks for issue.