This is mostly just the offapi/ part, more C++ code can be removed in
xmlsecurity/ after this. SignatureVerifier, SAXEventKeeper,
SignatureCreator, XMLSignatureTemplate and XMLEncryptionTemplate was
only used inside xmlsecurity, but they all are accessed directly
already. Decryptor and Encryptor wasn't even used by internal code since
they were added in commit 9f34fde7
(libxmlsec, 2004-07-12).

It seems to be unlikely that any of these non-published services were
used by 3rd-party code, since they were specific to other xmlsecurity/
code, not generic functionality that could be useful in other contexts.

Change-Id: I4bcfa88d11d2b92a440f6617193c6460125ce4fd
Reviewed-on: https://gerrit.libreoffice.org/33569Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>