Instead, use plain std::vector<SfxFrame*>.

Change-Id: Ib32e748a0ce744d15cbe48f5d03e28c57b731394
Reviewed-on: https://gerrit.libreoffice.org/43938Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>