[polymer] fix editor hints -- query/queryAll and unused imports

pkg/polymer/test/attr_mustache_test.dart

Index: pkg/polymer/test/attr_mustache_test.dart
diff --git a/pkg/polymer/test/attr_mustache_test.dart b/pkg/polymer/test/attr_mustache_test.dart
index 45da52523e279d8af2411a2abd654cd51b6fd4fd..e327ed6782689458fa64d9cfebf911b9d7d15303 100644
--- a/pkg/polymer/test/attr_mustache_test.dart
+++ b/pkg/polymer/test/attr_mustache_test.dart
@@ -51,8 +51,8 @@ main() {
   setUp(() => Polymer.onReady);
 
   test('mustache attributes', () {
-    final xtest = document.query('#test');
-    final xtarget = xtest.shadowRoot.query('#target');
+    final xtest = document.querySelector('#test');
+    final xtarget = xtest.shadowRoot.querySelector('#target');
     return xtarget.foundSrc;
   });
 }