Instead, just use std::vector<DdeItemImpData>.

Change-Id: If0c4943bdf370211cd6e0466a899da718480a4ae
Reviewed-on: https://gerrit.libreoffice.org/43415Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>