s390x/tcg: drop program_interrupt()

All users are gone, we can finally drop it and make sure that all new
program interrupt injections are reminded of the retaddr - as they have to
use s390_program_interrupt() now.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20171130162744.25442-16-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
