This is mostly just the offapi/ part, more C++ code can be removed in
xmlsecurity/ after this.

It seems to be unlikely that this non-published service was used by 3rd-party
code, since it was specific to other xmlsecurity/ code, not generic
functionality that could be useful in other contexts.

Change-Id: I0d798577a42445e65a4c5178fcb4464ea03bc56e
Reviewed-on: https://gerrit.libreoffice.org/46442Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>