Fix test environment settings
The testing infrastructure in SMTK is trying to be clever, but only ends up getting in the way. External modules should just be expected to work with
import foo. The only environment manipulation that should occur is to get the
smtk module itself into
PYTHONPATH. This is screwing up the superbuild because it tries to put things like ParaView and the local-built Python into
PYTHONPATH, but ends up getting shut out by the test environment logic.