since it has nothing to do with the headless command line option, so
use the name it has in the configure.ac file

Change-Id: Ibf0615ed02695d6e48a797f5632e4f417c010c70
Reviewed-on: https://gerrit.libreoffice.org/59611
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>