qapi job: Elide redundant has_FOO in generated C

The has_FOO for pointer-valued FOO are redundant, except for arrays.
They are also a nuisance to work with.  Recent commit "qapi: Start to
elide redundant has_FOO in generated C" provided the means to elide
them step by step.  This is the step for qapi/job.json.

Said commit explains the transformation in more detail.  The invariant
violations mentioned there do not occur here.

Cc: John Snow <jsnow@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Cc: qemu-block@nongnu.org
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-Id: <20221104160712.3005652-15-armbru@redhat.com>