This policy suppresses deprecated bits in output, and thus permits
"testing the future".  Implement it for QMP command query-qmp-schema:
suppress information on deprecated commands, events and object type
members, i.e. anything that has the special feature flag "deprecated".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-8-armbru@redhat.com>