Bug 18069: Remove residue of rebuild_zebra -x

Bug 18069: Remove residue of rebuild_zebra -x

Bug 17731 removed the -x option of rebuild_zebra but koha-rebuild-zebra
still cals the script with this option.

"Warning: You passed -x which is already the default and is now deprecated"

Test plan:
sudo koha-rebuild-zebra -f
should no longer raise the warning

Signed-off-by: Mason James <mtj@kohaaloha.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>