Remove various ifdefs for old Qt + KF5 versions
Another 3-pack of related clean-ups:
Remove remaining ifdefs for Qt 5 support
A few unrelated lines got reformatted by clang-format, too.
Remove an ifdef for QWaylandClient support < Qt 6.2
At the time of writing, the minimum requirement is already Qt 6.4.
Remove ifdefs for old-school KF5 KAuth includes