dns/libdjbdns: Deprecate and set expiration date to 2023-06-30

Project hasn't been centrally managed since last release in 2001 and
there are various third party patches to keep it somewhat relevant with
todays standards. Port has also been unmaintained since last
maintainer stepped down in 2008.

dns/libdjbdns/Makefile

@@ -9,6 +9,9 @@ MAINTAINER=	ports@FreeBSD.org
 COMMENT=	Public domain DNS client library
 WWW=		https://cr.yp.to/djbdns/dns.html
 
+DEPRECATED=	No longer compliant with current DNS standards and source code hasn't been centrally managed for over 20 years
+EXPIRATION_DATE=2023-06-30
+
 USES=		gmake
 
 USE_LDCONFIG=	yes