Implement a proper license check test in qtqa module

The qtqa module currently has a very basic license check in tests/auto/headers.

This should be extended or replaced with a more complete check along the lines of the check used in Qt4 CI.

Since we already have a full perl setup in qtqa, and such a text processing task is typically much easier to implement in perl than C++, suggest ditching the license check from tst_headers altogether and reimplementing a new script. (Note, the Qt4 license check is not particularly maintainable either so I would prefer not porting that.)