Removing the main link to Jetpack from the menu

Try this instead:

function remove_posts_menu() {
    if ( ! current_user_can( 'manage_options' ) ) 
        remove_submenu_page( 'jetpack', 'jetpack' );

}
add_action( 'admin_init', 'remove_posts_menu' );

where the menu slug and submenu slug are jetpack.