WooCommerce - Remove the "Related Products" section from a template by removing the related posts query arguments.

gistfile1.php

<?php
/*
 * wc_remove_related_products
 * 
 * Clear the query arguments for related products so none show.
 * Add this code to your theme functions.php file.  
 */
function wc_remove_related_products( $args ) {
	return array();
}
add_filter('woocommerce_related_products_args','wc_remove_related_products', 10); 

In WooCommerce 3.0 this will not work.

Working code (assuming that you use the default WooCommerce template):

add_action( 'init', 'woocommerce_remove_related_products' );
function woocommerce_remove_related_products() {
	remove_action( 'woocommerce_after_single_product_summary', 'woocommerce_output_related_products', 20 );
}