cleanup imports (#2045)

diff --git a/tool/bot/rule_doc_check.dart b/tool/bot/rule_doc_check.dart
index 4f89b63..56b22b5 100644
--- a/tool/bot/rule_doc_check.dart
+++ b/tool/bot/rule_doc_check.dart
@@ -3,16 +3,11 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:convert';
-import 'dart:io';
 
 import 'package:http/http.dart' as http;
-import 'package:linter/src/analyzer.dart';
-import 'package:linter/src/rules.dart';
-import 'package:pub_semver/pub_semver.dart';
 import 'package:test/test.dart';
 
 import '../crawl.dart';
-import '../since.dart';
 
 void main() async {
   print('Getting latest linter package info from pub...');