shotwell Build-Depends on libappstream-glib-dev, but does not link to
the appstream-glib library, and the build-dependency appears to be
unused. This is one of only two remaining packages preventing the
removal of appstream-glib (the other is transmission).

Please consider the attached patch. I have confirmed using diffoscope
that when I rebuild shotwell with and without this patch, the results
are identical. I didn't test the resulting binaries beyond that (I don't
use this package myself).

Thanks,
    smcv

     smcv