and drop unused E_HELPBOOKMARKS

Change-Id: I5756ea326bdc1a99f7d6f1ba43baf6aca9f7f2fc
Reviewed-on: https://gerrit.libreoffice.org/36728Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>