interfaces: don't use the DBus DTD
interfaces: don't use the DBus DTD

We don't include this file in the source, and it won't validate anyway because
of the documentation extensions.

ThomasBollmeier/libsocialweb-flickr-oauth,lcp/libsocialweb,GNOME/libsocialweb,GNOME/libsocialweb,lcp/libsocialweb,GNOME/libsocialweb,ThomasBollmeier/libsocialweb-flickr-oauth,ThomasBollmeier/libsocialweb-flickr-oauth,lcp/libsocialweb