Remove dependency on phpoffice/phpexcel

We seem to be running into the same issue in our project.

There is a migration guide to help with moving to phpoffice/phpspreadsheet:
https://phpspreadsheet.readthedocs.io/en/latest/topics/migration-from-PHPExcel/

unqunq → changed the visibility of the branch 3423921-update-dependency to hidden.

@sboden → Would you be able to test, please?

I tested the fix provided by @unqunq and exporting to xlsx is working fine.

It's ok now. This one can be closed.
Thanks.