We don't use Texinfo any more; we can remove the references to the
.texi source file from our git.orderfile.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200925162316.21205-20-peter.maydell@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>