[Spike] Refactor updater tests

[sssoleileraaa]

Description

There is some confusion around how the launcher tests work because of how we try to automatically detect OS version and support both 4.0 and 4.1 as well as pyqt4 and pyqt5 and bullseye ad buster... let's look into simplifying and removing test support for stuff we don't need to support anymore after August 4th.

It might help to explain what it is we are actually testing as well (I think just the GUI, right?).

[rocodes]

Yes, the pyqt4/5 dual support was just for supporting 4.0 dom0 (pyqt4) vs other environments (like testing or 4.1 dom0 - pyqt5), so there's a lot we can remove now that we're on 4.1.

[zenmonkeykstop]

This should be revisited to see if we can drop further stuff now we're 4.2 only.

[zenmonkeykstop]

Keeping for now - updater tests can be 4.2-only etc as we don't support older versions of Qubes.