but we can remove the whole setting pixels one at a time
because the format matches N8BitPal, and typically that's
what we're writing to anyway, so a direct copy will do

Change-Id: I91c72ec37055eb064d84461ac89b6bf171ef8d79
Reviewed-on: https://gerrit.libreoffice.org/35442Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>