CodeReview.md: remove RELNOTE=

Remove the description of the RELNOTE= CL directive.
It is no longer supported.

Change-Id: Id96f44ce98ae056cbe78398c494ead76461635bf
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/581723
Commit-Queue: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/CodeReview.md b/CodeReview.md
index 9a0835a..1f98c14 100644
--- a/CodeReview.md
+++ b/CodeReview.md
@@ -17,7 +17,6 @@
 # CL Directives
 
 * `R=foo` — assign a reviewer within the [Go CL dashboard](https://swtch.com/godash/)
-* `RELNOTE=yes` or `RELNOTE=<subject>` — tag for release notes; scraped by the [relnote](https://golang.org/x/build/cmd/relnote) tool
 * `DO NOT SUBMIT` (in the commit message) — block submission; see the "Work in progress" section below
 * `Updates #1234` or `Fixes #1234` (in the commit message) — link the CL from the GitHub issue and optionally close the issue after the CL is merged