util: fix removal of callbacks in virCloseCallbacksRun

util: fix removal of callbacks in virCloseCallbacksRun

The close callbacks hash are keyed by a UUID-string, but
virCloseCallbacksRun was attempting to remove them by raw UUID. This
patch ensures the callback entries are removed by UUID-string as well.

This bug caused problems when guest migrations were abnormally aborted:

  # timeout --signal KILL 1 \
      virsh migrate example qemu+tls://remote/system \
        --verbose --compressed --live --auto-converge \
        --abort-on-error --unsafe --persistent \
        --undefinesource --copy-storage-all --xml example.xml
  Killed

  # virsh migrate example qemu+tls://remote/system \
      --verbose --compressed --live --auto-converge \
      --abort-on-error --unsafe --persistent \
      --undefinesource --copy-storage-all --xml example.xml
  error: Requested operation is not valid: domain 'example' is not being migrated

Signed-off-by: Michael Chapman <mike@very.puzzling.org>