It was extended by "seru" in 8d190244. This person could not be reached
(or does not reply), and it's in the way of LGPL relicensing. Deprecate
it, and mark the (probably) affected parts of the code with HAVE_GPL. To
be fair, even though the osd.c parts were refactored from the original
code, there's probably no copyright by seru on it. But for now play it
save. The mere existence of a 3rd OSD level is certainly not
copyrightable, so you still can set osd-level to 3 - just that it does
nothing.
6ddd95fd6a