www/mod_xmlns: Deprecate and set expiration date to 2022-03-31

Upstream called it "provisionally stable" back in 2004 and no
further development

Reference: http://apache.webthing.com/mod_xmlns/

Approved by:	tcberner (mentor)
Differential Revision:	https://reviews.freebsd.org/D32397

www/mod_xmlns/Makefile

@@ -13,6 +13,9 @@ COMMENT=	Apache module for XML namespaces
 
 LICENSE=	GPLv2
 
+DEPRECATED=	Abandoned upstream, last release in 2004
+EXPIRATION_DATE=2022-03-31
+
 USE_GNOME=	libxml2
 USES=		apache:2.2+ gnome