You can remove the entirety of the /Classes/PHPExcel/Shared/PDF folder and it won't cause any problems.... as long as you don't try writing to PDF. There are no licencing issues with doing this, and it frees a lot of disk space (if this is critical).
If you wanted to really clean everything up, you could also delete /Classes/PHPExcel/Writer/PDF.php as well. There are PDF references in /Classes/PHPExcel/Writer/HTML.php, but you shouldn't need to worry about these.
polling for whether we should retain tcPDF as part of the PHPExcel distribution, or simply provide a set of wrappers to the more popular PDF writer classes (allowing developers to install their preferred PDF writer library independently and simply configure
PHPExcel to work with that)... but so far I have had absolutely no feedback at all.