docs: site-example: remove redundant "iptables" package

iptables will be pulled in anyways.

docs/site-example/site.mk

@@ -25,7 +25,6 @@ GLUON_SITE_PACKAGES := \
 	gluon-setup-mode \
 	gluon-status-page \
 	haveged \
-	iptables \
 	iwinfo
 
 ##	DEFAULT_GLUON_RELEASE