tests: qemublocktest: fix crashing with SIGBUS

Commit bcbb026993 converted qemublocktest to use
g_autoptr for virQEMUCaps. To prevent it from crashing,
don't explicitly call virObjectUnref() on this object.

Signed-off-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

tests/qemublocktest.c

@@ -1394,7 +1394,6 @@ mymain(void)
  cleanup:
     qemuTestDriverFree(&driver);
     VIR_FREE(capslatest_x86_64);
-    virObjectUnref(caps_x86_64);
 
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }