internal: fix megacheck warnings (#14919)

internal/jsre/pretty.go

@@ -65,14 +65,6 @@ func prettyError(vm *otto.Otto, err error, w io.Writer) {
 	fmt.Fprint(w, ErrorColor("%s", failure))
 }
 
-// jsErrorString adds a backtrace to errors generated by otto.
-func jsErrorString(err error) string {
-	if ottoErr, ok := err.(*otto.Error); ok {
-		return ottoErr.String()
-	}
-	return err.Error()
-}
-
 func (re *JSRE) prettyPrintJS(call otto.FunctionCall) otto.Value {
 	for _, v := range call.ArgumentList {
 		prettyPrint(call.Otto, v, re.output)