remove unused code from writerfilter

Not sure whether void OOXMLFastHelper<T>::mark(OOXMLFastContextHandler * pHandler, Id nId, const OUString & rValue) is really unused (tested on linux build seems to be unused).
If it IS unused the commit should NOT be included and writerfilter::ooxml::OOXMLFastContextHandler::mark(unsigned int const&, boost::shared_ptr<writerfilter::ooxml::OOXMLValue>) is to be put into unusedcode.exclude.


Change-Id: I5ae08427e62f89df3d4112486837d8eb5fa752f0
Reviewed-on: https://gerrit.libreoffice.org/7327
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>