How to Hide the "Uni-theme Maintenance Plugin" Admin Menu

function plt_hide_uni_theme_maintenance_mode_menus() {
	//Hide the "Settings → Uni-theme Maintenance Plugin" menu.
	remove_submenu_page('options-general.php', 'unitheme-maintenance-options-page');
}

add_action('admin_menu', 'plt_hide_uni_theme_maintenance_mode_menus', 11);

Where do I put this code?