fix(offline_install): remove sysconfdir option of install script
fix(offline_install): remove sysconfdir option of install script

install.sh scripts can choose right directory for different distros in
different install mode (regular, root/nonroot offline). So we don't need
this option in SCT.

Signed-off-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>

scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests