Kai Koehne authored Dec 07, 2021 and Kai Koehne committed Dec 19, 2021

This is in line with e.g. qtbase. Also remove outdated/unreferenced
license files.

Pick-to: 6.3
Change-Id: I5d3370ab453610f9c8165ff9e57db7ad4a785370
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>