You have to add the following CSS to an admin.css file (name it whatever you like but it has to be a css file that applies to the admin.
You need the following in that file:
.order-lower-indicator,
.order-higher-indicator{
display:none;
}
To enqueue a stylesheet properly in the admin:
https://developer.wordpress.org/reference/hooks/admin_enqueue_scripts/
It’s the same basic process as enqueuing for the front end but you’re just applying a different action: do_action( 'admin_enqueue_scripts', string $hook_suffix );