UPDATE: useless from 2.0.4+ thanks to the new filter disable_variation_duplicator_for_woocommerce_image_clone

variation-duplicator-for-woocommerce-disable-image-duplicator.php

<?php
/**
 * Plugin Name: Duplicate Variations for WooCommerce (Disable Image Duplicator)
 * Description: Disattiva la funzionalità di "image duplicator" che rallenta il loading delle variazioni
 * Author: Mirco Babini
 * Domain Path: /languages
 * Version: 2.0.3
 * Author URI: https://sedweb.com/
 */
add_action( 'variation_duplicator_for_woocommerce_variation_image_clone_loaded', function ( $instance ) {
	remove_action( 'woocommerce_product_after_variable_attributes', array( $instance, 'form' ), 10 );
	remove_action( 'woocommerce_save_product_variation', array( $instance, 'prepare' ) );
	remove_action( 'woo_variation_duplicator_load_variations', array( $instance, 'notice' ) );
} );