unused XLinkFactory stuff

[Caolán McNamara]

unusedcode.easy has an
OooEmbeddedObjectFactory::createInstanceLinkUserInit after the recent
devirtualization allowed callcatcher to determine that its unused. On
investigation the embeddedobj/source/commonembedding/xfactory.hxx used
to explicitly list implementing XLinkFactory until 

251f1b0b38be7d1267339898e44e320f05849e22
Date:   Tue Jan 8 14:29:06 2013 +0200
    fdo#46808, Adapt embed::*EmbeddedObjectCreator UNO services to new
style

interface XEmbeddedObjectCreator
{
    interface XEmbedObjectCreator;
    interface XEmbedObjectFactory;
    interface XLinkCreator;
    [optional] interface XLinkFactory;
};

so I assume the problem here is the [optional] thing. What's the right
way to fix this within the new style uno foo ?

C.