Fix the sys.geom.class.multipath.misc.fail_on_error test on stable/12

This test uses a gnop feature (delay probability) that isn't available on
stable/12. But it's unnecessary; the test works fine without it. Removing
it simplifies the test and, once MFCed, will allow it to pass on stable/12.

PR: 244158
Reported by: lwhsu
MFC after: 2 weeks