suzerain: ignore rho2_om_om

I see errors in this like O(1e-15) relative to the prior
solutions.  I have been unable to tease out anything wrong
and so, rather than update gold solutions, I'm documenting
this hiccup here.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45124 0bd85f0b-c151-43b9-a1e9-27231104551f