this reverts

    commit a20ec3b5
    fix iterator invalidation assert
and
    commit 4a290888
    SvtBroadcaster unify the normal and PrepareForDestruction paths

no idea what is going on, I suspect that std::vector is re-allocating
its data buffer despite having called reserve()

Change-Id: I681ae5fca4578240a2a0dc0af51ff06d919f9099
Reviewed-on: https://gerrit.libreoffice.org/61464
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>