Copy and paste the following code in the functions.php of your current theme to remove the tracking details when woocommerce order is marked completed.

function remove_my_action() {
	remove_action('woocommerce_email_before_order_table', array( 'WPCWOO_P2P', 'before_order_table_email') );
	remove_action( 'woocommerce_order_details_before_order_table', array( 'WPCWOO_P2P', 'before_order_table' ) );
}
add_action( 'admin_init', 'remove_my_action' );