Revert "suzerain: new-style 'use mpi'"

This reverts commit 0cbbfd78ccd08a13b298199b94a4e6108f4e68ca.
Turns out to cause build issues due to mismatched modules on some target systems.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44147 0bd85f0b-c151-43b9-a1e9-27231104551f