A user ran into an issue while upgrading where
ContentType.objects.get(model="realmreactivationstatus",
app_label="zerver") fails due to the object being missing. The reason
for that is to be yet figured out, but the immediate solution is clear
in the sense that the migration can just quit early
if not Confirmation.objects.filter(type=REALM_REACTIVATION).exists() and
that'll effectively skip it for almost all servers (because realm
reactivations links are something that's really only useful on Zulip
Cloud).
