Filter to hide the order_comments on the checkout page.

functions.php

/* 
* Code installation instructions:
* 1. Copy the below code.
* 2. Open your child theme's functions.php file.
* 3. Paste the copied code at the very bottom of it & save the file OR upload it on your server/hosting.
*/

/*
* Filter to hide the order_comments on the checkout page.
*/

add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );

function custom_override_checkout_fields( $fields ) {
     unset($fields['order']['order_comments']);

     add_filter( 'woocommerce_enable_order_notes_field', '__return_false' );
     return $fields;
}