qemu: blockjob: Remove infrastructure for remembering to delete image

Now that we delete the images elsewhere it's not required. Additionally
it's safe to do as we never released an upstream version which required
this being in place.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

tests/qemustatusxml2xmldata/backup-pull-in.xml

@@ -248,7 +248,6 @@
           </privateData>
         </source>
       </store>
-      <deleteStore/>
     </blockjob>
   </blockjobs>
   <agentTimeout>-2</agentTimeout>