ipatests: remove xfail from test_dnssec
The nightly test test_dnssec.py::TestInstallDNSSECFirst::test_chain_of_trust
used to fail because of https://github.com/rthalley/dnspython/issues/343,
but the issue has been fixed upstream and does not happen any more since
PRCI is using python3-dns-1.16.0-7.
Remove the xfail.
Reviewed-By: Mohammad Rizwan Yusuf <myusuf@redhat.com>