Drop effective top level domain for `au.securedrop.tor.onion`

In #41831 (closed) we want to add an exception for abc.au.securedrop.tor.onion by listing au.securedrop.tor.onion as a top level domain in effective_tld_names.dat.

In the SecureDrop tor.onion directory they plan on eventually migrating this exception to no longer use a sub-domain: https://github.com/freedomofpress/securedrop-https-everywhere-ruleset/issues/219.

Once the migration is complete we can drop the exception on our end.

Marking this as "15.0" in the case the migration can occur then, otherwise we can keep bumping the version as needed.