delete_in_topic: Name unused variable as ignored.
delete_in_topic: Name unused variable as ignored.

sub isn't used, so let's just call it ignored_sub to be explicit about
that intent.

zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip