qemu: Remove stale comment outlining how to extend qemuDomainBlockPivot

With -blockdev:

- we track the job and check it after restart
- have the ability to ask qemu to persist it to collect result
- have the ability to report errors.

This solves all points the comment outlined so remove it. Also all jobs
handle the disk state modification along with the event so there's
nothing special the comment says.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_driver.c

@@ -17007,16 +17007,6 @@ qemuDomainBlockPivot(virQEMUDriverPtr driver,
         goto cleanup;
     }
 
-    /* Attempt the pivot.  Record the attempt now, to prevent duplicate
-     * attempts; but the actual disk change will be made when emitting
-     * the event.
-     * XXX On libvirtd restarts, if we missed the qemu event, we need
-     * to double check what state qemu is in.
-     * XXX We should be using qemu's rerror flag to make sure the job
-     * remains alive until we know its final state.
-     * XXX If the abort command is synchronous but the qemu event says
-     * that pivot failed, we need to reflect that failure into the
-     * overall return value.  */
     qemuDomainObjEnterMonitor(driver, vm);
     if (blockdev)
         ret = qemuMonitorJobComplete(priv->mon, job->name);