sumdb/note: delete chop

CL 720581 replaced almost all instances of it, this gets the last one.

[git-generate]
cd sumdb/note
rf '
	ex { import "strings"; chop -> strings.Cut }
	rm chop
'

Change-Id: I3bd4665c959c7b6fd2729189a6e7cfb101e5a4b7
Reviewed-on: https://go-review.googlesource.com/c/mod/+/720700
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
diff --git a/sumdb/note/note.go b/sumdb/note/note.go
index 8b2b252..c95777f 100644
--- a/sumdb/note/note.go
+++ b/sumdb/note/note.go
@@ -273,13 +273,6 @@
 	return v, nil
 }
 
-// chop chops s at the first instance of sep, if any,
-// and returns the text before and after sep.
-// If sep is not present, chop returns before is s and after is empty.
-func chop(s, sep string) (before, after string, ok bool) {
-	return strings.Cut(s, sep)
-}
-
 // verifier is a trivial Verifier implementation.
 type verifier struct {
 	name   string
@@ -553,7 +546,7 @@
 			return nil, errMalformedNote
 		}
 		line = line[len(sigPrefix):]
-		name, b64, _ := chop(string(line), " ")
+		name, b64, _ := strings.Cut(string(line), " ")
 		sig, err := base64.StdEncoding.DecodeString(b64)
 		if err != nil || !isValidName(name) || b64 == "" || len(sig) < 5 {
 			return nil, errMalformedNote