DISALLOW_FILE_MODS disables admin-menu

If you have a version-controlled wordpress,
you often have define( 'DISALLOW_FILE_MODS', true ); in your config.

Therefor the admins don’t have the capability update_core.

And as you check for that capability when deciding if you want to show the menu option or not, the menu isn’t shown for anybody.

jetpack-carousel.php:39: add_menu_page( ..., 'update_core', ... );
jetpack-carousel.php:41: add_submenu_page( ..., 'update_core', ... );