Remove unnecessary imports (dart-lang/watcher#104)

pkgs/watcher/lib/src/directory_watcher.dart

diff --git a/pkgs/watcher/lib/src/directory_watcher.dart b/pkgs/watcher/lib/src/directory_watcher.dart
index 043ebab..158b86b 100644
--- a/pkgs/watcher/lib/src/directory_watcher.dart
+++ b/pkgs/watcher/lib/src/directory_watcher.dart
@@ -8,7 +8,6 @@
 import 'custom_watcher_factory.dart';
 import 'directory_watcher/linux.dart';
 import 'directory_watcher/mac_os.dart';
-import 'directory_watcher/polling.dart';
 import 'directory_watcher/windows.dart';
 
 /// Watches the contents of a directory and emits [WatchEvent]s when something

pkgs/watcher/lib/src/file_watcher.dart

diff --git a/pkgs/watcher/lib/src/file_watcher.dart b/pkgs/watcher/lib/src/file_watcher.dart
index 9b8ecc4..143aa31 100644
--- a/pkgs/watcher/lib/src/file_watcher.dart
+++ b/pkgs/watcher/lib/src/file_watcher.dart
@@ -7,7 +7,6 @@
 import '../watcher.dart';
 import 'custom_watcher_factory.dart';
 import 'file_watcher/native.dart';
-import 'file_watcher/polling.dart';
 
 /// Watches a file and emits [WatchEvent]s when the file has changed.
 ///

pkgs/watcher/lib/src/resubscribable.dart

diff --git a/pkgs/watcher/lib/src/resubscribable.dart b/pkgs/watcher/lib/src/resubscribable.dart
index 1c4bb25..91f5090 100644
--- a/pkgs/watcher/lib/src/resubscribable.dart
+++ b/pkgs/watcher/lib/src/resubscribable.dart
@@ -5,7 +5,6 @@
 import 'dart:async';
 
 import '../watcher.dart';
-import 'watch_event.dart';
 
 /// A wrapper for [ManuallyClosedWatcher] that encapsulates support for closing
 /// the watcher when it has no subscribers and re-opening it when it's