Remove obsolete - and broken - wayland clipboard workaround

I am not sure, whether the code removed by this patch has actually been
needed at a time. At least for Qt 6.x, I could not find any direct
documentation to that effect.

At any rate, contrary to its intention, the removed code breaks
clipboard handling with Qt 6.10.2 on Wayland, at least (clipboard always
detected as empty), and removing it restores correct behavior.