Also remove the unused function strnccmp.

Change-Id: Ie857dfca1e52b1251f85abfba3cd0e12e509974f
Reviewed-on: https://gerrit.libreoffice.org/3888Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>