Fix server shutdown in bin/tests/system/run.sh

Fix server shutdown in bin/tests/system/run.sh

a4f0281962c8d8f80f6efc04cad550146eec8463 is a flawed backport of
cf5105939c1c1802e69cc63a39e9d71b6e5f67e1 - it retained the original
invocation of bin/tests/system/stop.pl in bin/tests/system/run.sh.  This
results in the former script being called twice for each system test,
which does not cause problems on Unix systems, but triggers false
positives about named instances dying prematurely on Windows.  Fix by
removing the offending invocation of bin/tests/system/stop.pl from
bin/tests/system/run.sh.