Fixes for simpler PHPOffice / PHPExcel installation

The module page says:

Installation:
For Bulk Content Operation to work, You must download PHP Excel Library and extract library into any libraries folder like sites/*/libraries or libraries in root folder of your Drupal 8 instance.

The attached patch removes code that forces the installation of the PHP Excel library in a different place than where Composer places it.

With this patch, simply run composer require phpoffice/phpexcel and everything will work as needed, without the need to move the library.