add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );

function custom_override_checkout_fields( $fields ) {

unset($fields['billing']['billing_first_name']);
unset($fields['billing']['billing_last_name']);
unset($fields['billing']['billing_company']);
unset($fields['billing']['billing_address_1']);
unset($fields['billing']['billing_address_2']);
unset($fields['billing']['billing_city']);
unset($fields['billing']['billing_postcode']);
unset($fields['billing']['billing_country']);
unset($fields['billing']['billing_state']);
unset($fields['billing']['billing_phone']);
unset($fields['order']['order_comments']);
unset($fields['account']['account_username']);

    return $fields;
}