(maint) Remove facter versions test

This test attempts to emulate various versions of facter, but is
still dependent on the version of facter it is running against. The
immediate symptom was that the test breaks with facter 2.0.1 because
it adds another external facts search directory.

I tried a couple ways to stub this but allowing it to pretend
to run against one set of facters, while actually running against
one real facter (which might itself be one of several versions)
eluded me.

So this patch just removes the test.