[applets/appmenu] Remove obsolete TODO comment
Reason for the change
frameworks/kguiaddons!125 fixes the limitation on Wayland
Test plan
Use global menu on Wayland, press Alt, see the underlined letters and use alt to navigate the menu
Screenshots or screen recordings
Bugs fixed
https://bugs.kde.org/show_bug.cgi?id=483657 is fixed by the kguiaddons change