Hygiene: remove outdated comment in footer.mustache

Remove old comment. I think this may have been referring `{{.}}` but
that's not present.

Change-Id: If2443027cfc2da970f4c986c6a85406161ee9173

includes/skins/footer.mustache

@@ -6,7 +6,6 @@
 	<div class="license">{{{licensehtml}}}</div>
 	{{#lists}}
 	<ul class="footer-{{name}} hlist hlist-separated">
-		{{! "." means "current context", which allows us to iterate over Plain Old PHP Arrays™. }}
 		{{#items}}<li id="footer-{{category}}-{{name}}">{{{linkhtml}}}</li>{{/items}}
 	</ul>
 	{{/lists}}