graphics/dspdfviewer: simplify logic for -Wno-error=extra-semi-stmt

I first bogusly added OSVERSION < 1300000 at the end, but in hindsight
and from looking at svnweb the version logic after 11.3 EOL is

v >= 1300014 || (v in 1104000 .. 1200000) || v >= 1201000

(v in 1104000 .. 1200000) || v >= 1201000

(v >= 1200000 && v < 1201000)

So the port should not relax the check on (early) 12.0, which we can as
well leave out.

While here, add a note about upstream #191 still being open.

Phabricator: D26646