runtime, unicode: use consistent banner for generated code

Per golang.org/s/generatedcode

Updates #nnn

Change-Id: Ia7513ef6bd26c20b62b57b29f7770684a315d389
Reviewed-on: https://go-review.googlesource.com/45470
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/runtime/sizeclasses.go b/src/runtime/sizeclasses.go
index e616e95..5366564 100644
--- a/src/runtime/sizeclasses.go
+++ b/src/runtime/sizeclasses.go
@@ -1,4 +1,4 @@
-// AUTO-GENERATED by mksizeclasses.go; DO NOT EDIT
+// Code generated by mksizeclasses.go; DO NOT EDIT.
 //go:generate go run mksizeclasses.go
 
 package runtime