libxo manpages: Fix unusual Xr order

[ziaee]

I think @des and I already fixed all of these upstream a while ago (along with many other manpage typos), however they merged it into a dev branch and I guess it's just rotting there?

[ziaee]

I was wrong, sorry. They did make it into the release, and importing the release is open for review here: https://reviews.freebsd.org/D59882

[wosch]

Most Xr problems are already fixed in D59882, closing.