gorelease: remove dependence on xerrors

Change-Id: I46fc0b940ef4e429a2afa6880151289a7c9a3c62
Reviewed-on: https://go-review.googlesource.com/c/exp/+/357618
Trust: Jonathan Amsterdam <jba@google.com>
Trust: Jean de Klerk <deklerk@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jean de Klerk <deklerk@google.com>
diff --git a/cmd/gorelease/errors.go b/cmd/gorelease/errors.go
index e0ebd1e..d99f840 100644
--- a/cmd/gorelease/errors.go
+++ b/cmd/gorelease/errors.go
@@ -12,7 +12,6 @@
 	"strings"
 
 	"golang.org/x/mod/module"
-	"golang.org/x/xerrors"
 )
 
 type usageError struct {
@@ -27,7 +26,7 @@
 
 func (e *usageError) Error() string {
 	msg := ""
-	if !xerrors.Is(e.err, flag.ErrHelp) {
+	if !errors.Is(e.err, flag.ErrHelp) {
 		msg = e.err.Error()
 	}
 	return usageText + "\n" + msg + "\nFor more information, run go doc golang.org/x/exp/cmd/gorelease"