suzerain: #2599 remove Abs

The presence of Abs breaks the symbolic replacement foo.
It is there for numerical but not derivation reasons,
so nuke it.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44120 0bd85f0b-c151-43b9-a1e9-27231104551f