WooCommerce hide all shipping options when free shipping is available

wc_hide_all_shipping_when_free_available.php

<?php
add_filter( 'woocommerce_available_shipping_methods', 'hide_standard_shipping_when_free_is_available' , 10, 1 );
function hide_standard_shipping_when_free_is_available( $available_methods ) {
    if( isset( $available_methods['free_shipping'] ) ) {
      $methods = $available_methods;
 		foreach( $methods as $key => $method ) {
 			if ( $key <> 'free_shipping' )
 				unset( $available_methods[$key] );
 		}
    }
    return $available_methods;
}
?>