blockdev: Drop deprecated bogus -drive interface type

Drop the crap deprecated in commit a1b40bda "blockdev: Deprecate
-drive with bogus interface type" (v5.1.0).

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20210309161214.1402527-5-armbru@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>