Remove dead reference to Comments concept

Looks like a never-finished WIP.

Change-Id: I6a0dacfa233f0cc47b2833dcfc3f635372a110c3
diff --git a/Documentation/concept-changes.txt b/Documentation/concept-changes.txt
index 762fb43..6de787c 100644
--- a/Documentation/concept-changes.txt
+++ b/Documentation/concept-changes.txt
@@ -14,7 +14,7 @@
 
 * Current and previous patch sets
 * <<Change properties>>, such as owner, project, and target branch
-* link:CONCEPT-comments.html[Comments]
+* Comments
 * Votes on link:config-labels.html[Review Labels]
 * The <<change-id>>