cmd/relnote: use GerritCL.Subject method instead of clSubject function

Apply a trivial code simplification. Tested by re-running relnote, and
its output did not change.

For golang/go#41849.

Change-Id: Ifffebca5ee55d7470f32a2469b4e41d1a1a458d1
Reviewed-on: https://go-review.googlesource.com/c/build/+/272906
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
diff --git a/cmd/relnote/relnote.go b/cmd/relnote/relnote.go
index ebde350..e6d4064 100644
--- a/cmd/relnote/relnote.go
+++ b/cmd/relnote/relnote.go
@@ -35,7 +35,7 @@
 }
 
 func (c change) TextLine() string {
-	subj := clSubject(c.CL)
+	subj := c.CL.Subject()
 	if c.Note != "yes" && c.Note != "y" {
 		subj = c.Note + ": " + subj
 	}
@@ -123,7 +123,7 @@
 				pkg, "/pkg/"+pkg+"/", pkg)
 			for _, change := range changes[pkg] {
 				changeURL := fmt.Sprintf("https://golang.org/cl/%d", change.CL.Number)
-				subj := clSubject(change.CL)
+				subj := change.CL.Subject()
 				subj = strings.TrimPrefix(subj, pkg+": ")
 				fmt.Printf("\n    <p><!-- CL %d -->\n      TODO: <a href=%q>%s</a>: %s\n    </p>\n",
 					change.CL.Number, changeURL, changeURL, html.EscapeString(subj))
@@ -141,20 +141,10 @@
 	}
 }
 
-// clSubject returns the first line of the CL's commit message,
-// without the trailing newline.
-func clSubject(cl *maintner.GerritCL) string {
-	subj := cl.Commit.Msg
-	if i := strings.Index(subj, "\n"); i != -1 {
-		return subj[:i]
-	}
-	return subj
-}
-
 // clPackage returns the package name from the CL's commit message,
 // or "??" if it's formatted unconventionally.
 func clPackage(cl *maintner.GerritCL) string {
-	subj := clSubject(cl)
+	subj := cl.Subject()
 	if i := strings.Index(subj, ":"); i != -1 {
 		return subj[:i]
 	}