Remove phpspreadsheet dependency, recommend civiexportexcel instead
For most installs, running the advimport and civiexportexcel extensions will result in a PHP library conflict, because they both ship with phpSpreadsheet.
The simplest would be to recommend (but not require) the excel extension, a bit like the Stripe extension does. Not everyone needs the excel extension (custom imports can be done with the plain CSV importer).
Related: #9 (closed)