qapi block: 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/block*.json.

Said commit explains the transformation in more detail.

There is one instance of the invariant violation mentioned there:
qcow2_signal_corruption() passes false, "" when node_name is an empty
string.  Take care to pass NULL then.

The previous two commits cleaned up two more.

Additionally, helper bdrv_latency_histogram_stats() loses its output
parameters and returns a value instead.

Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Hanna Reitz <hreitz@redhat.com>
Cc: qemu-block@nongnu.org
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20221104160712.3005652-11-armbru@redhat.com>
[Fixes for #ifndef LIBRBD_SUPPORTS_ENCRYPTION and MacOS squashed in]

blockjob.c

@@ -354,7 +354,6 @@ BlockJobInfo *block_job_query_locked(BlockJob *job, Error **errp)
     info->auto_finalize = job->job.auto_finalize;
     info->auto_dismiss  = job->job.auto_dismiss;
     if (job->job.ret) {
-        info->has_error = true;
         info->error = job->job.err ?
                         g_strdup(error_get_pretty(job->job.err)) :
                         g_strdup(strerror(-job->job.ret));
@@ -414,7 +413,6 @@ static void block_job_event_completed_locked(Notifier *n, void *opaque)
                                         progress_total,
                                         progress_current,
                                         job->speed,
-                                        !!msg,
                                         msg);
 }