storefront theme has its own file where you can find all hooks and filters its adding for woocommerce.
you can find it at this path: storefront/inc/woocommerce/storefront-woocommerce-template-hooks.php
To remove storefront-sorting div, you can add the following in your child theme’s functions.php:
remove_action( 'woocommerce_after_shop_loop','storefront_sorting_wrapper',9 ); //.storefront-sorting opening after products loop
remove_action( 'woocommerce_after_shop_loop','storefront_sorting_wrapper_close',31 ); //.storefront-sorting closing after products loop
remove_action( 'woocommerce_before_shop_loop','storefront_sorting_wrapper',9 );//.storefront-sorting opening before products loop
remove_action( 'woocommerce_before_shop_loop','storefront_sorting_wrapper_close',31 ); //.storefront-sorting closing before products loop