check-database-compatibility: Ignore guardian, django.contrib.sites.
check-database-compatibility: Ignore guardian, django.contrib.sites.

We can safely ignore the presence of the extra tables that could be
left behind in the database from when we had these installed (before
Zulip 1.7.0 and 2.0.0, respectively).

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulip.com>

andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,kou/zulip,kou/zulip,rht/zulip,andersk/zulip,rht/zulip,kou/zulip,zulip/zulip,zulip/zulip,rht/zulip,kou/zulip,andersk/zulip,andersk/zulip,andersk/zulip,zulip/zulip,zulip/zulip,rht/zulip,zulip/zulip,kou/zulip,rht/zulip,andersk/zulip,zulip/zulip,kou/zulip,andersk/zulip,kou/zulip