and remove unused SV_ITEM_ID_EXTENDRLBOXSTRING

Change-Id: Ic84d9341d0225b01b9ef46814483c66b1af307b5
Reviewed-on: https://gerrit.libreoffice.org/28397Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>