qapi: Implement deprecated-output=hide for QMP events

This policy suppresses deprecated bits in output, and thus permits
"testing the future".  Implement it for QMP events: suppress
deprecated ones.

No QMP event is deprecated right now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-5-armbru@redhat.com>
2 files changed