Hide free shipping options' labels

functions.php

<?php 
// Paste everything below this line to your theme's functions.php file.

// Hide free shipping options prices. 
// Example:
// — Free Shipping: $0.00   => Free Shipping
// — Regular Shipping: $20  => Regular Shipping: $20
add_filter('woocommerce_cart_shipping_method_full_label', function($label, WC_Shipping_Rate $rate) {
    if (isset($rate->cost) && (float)$rate->cost === 0.0) {
        list($label,) = explode(':', $label, 2);
    }
    return $label;
}, 99, 2);