sys-apps/systemd: Also delete the /etc/issue line

systemd will ignore any lines that are repeated. We need to get rid
of this instance of /etc/issue, so that we can add our own.

Our /etc/issue is shipped here:
https://github.com/flatcar-linux/init/blob/flatcar-master/configs/tmpfiles.d/issuegen.conf

sdk_container/src/third_party/coreos-overlay/sys-apps/systemd/systemd-9999.ebuild

@@ -423,7 +423,8 @@ multilib_src_install_all() {
 	rm -rf "${ED}"/usr/share/factory
 	sed -i "${ED}"/usr/lib/tmpfiles.d/etc.conf \
 		-e '/^C!* \/etc\/nsswitch\.conf/d' \
-		-e '/^C!* \/etc\/pam\.d/d'
+		-e '/^C!* \/etc\/pam\.d/d' \
+		-e '/^C!* \/etc\/issue/d'
 }
 
 migrate_locale() {