Change OSD SW label

[MrD-RC]

The OSD SW label is not the most helpful. It seems to trip up quite a few new people to iNav.

Perhaps is should be changed to OSD OFF, as when active, the OSD is turned OFF?

[mattcave]

Found this Issue whilst searching “WTF does OSD SW do in iNav”. I think labelling it OSD OFF would have prevented me from having to search. I expected that it would cycle through the different alternative OSD layouts.