Remove commented code in OutputDevice::ReMirror

The following code was reimplemented in a cleaner fashion some time
ago. However, it was just commented out and never removed. There is
no need for it now, so removing. It's in the DVCS if it's really
needed :-)

Change-Id: Ia7d3c480ba70ccbd8dcf2808d9b712499c4cef4f
Reviewed-on: https://gerrit.libreoffice.org/7913
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>