ssh: remove custom contains, use slices.Contains

Change-Id: If4784469e7285675bdd51399a76bdc16f0036a2e
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/703635
Reviewed-by: Mark Freeman <markfreeman@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

ssh/client_auth_test.go

@@ -14,6 +14,7 @@ import (
 	"net"
 	"os"
 	"runtime"
+	"slices"
 	"strings"
 	"testing"
 )
@@ -1214,7 +1215,7 @@ func (cb configurablePublicKeyCallback) auth(session []byte, user string, c pack
 	if err != nil {
 		return authFailure, nil, err
 	}
-	if success == authSuccess || !contains(methods, cb.method()) {
+	if success == authSuccess || !slices.Contains(methods, cb.method()) {
 		return success, methods, err
 	}