Drop the rndc "-t" option from shudown system test
BIND 9.18 rndc does not know about the "-t" option, that results in an silent "invalid argument" error.
----------------------------- Captured stderr call -----------------------------
lt-rndc: invalid argument -t
Usage: lt-rndc [-b address] [-c config] [-s server] [-p port]
[-k key-file ] [-y key] [-r] [-V] [-4 | -6] command
The "-t" option originally came with 184eddb5 (a backport from the main branch).