schifra: mark as broken

There are many build failures caused by schifra, due to upstream
changing the tarball without doing new releases. Since has been an
on-going problem for some time, and is now the #1 issue in the
autobuilders. So let's mark this package broken, until someone cares
enough to fix it, or until we remove it.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>