[scripts] testnexus.py argument removed
Stress tests no longer work with nexus writer as a process (because the writer does not writer if SCAN_SAVING.writer!="nexus"). Argument was already removed for that but still used.
Stress tests no longer work with nexus writer as a process (because the writer does not writer if SCAN_SAVING.writer!="nexus"). Argument was already removed for that but still used.