Fixing a bunch of dartc errors in dart:html tests.

tests/html/node_test.dart

Index: tests/html/node_test.dart
diff --git a/tests/html/node_test.dart b/tests/html/node_test.dart
index 01ac3c3a188c7b8a1abaaaf30a7f428cdd3165e9..5a406cf6d4d99661c75e91be1a547a9d950d091c 100644
--- a/tests/html/node_test.dart
+++ b/tests/html/node_test.dart
@@ -41,8 +41,7 @@ main() {
   test('remove', () {
     final node = makeNodeWithChildren();
     final subnode = node.nodes[1];
-    final out = subnode.remove();
-    expect(out, isNull);
+    subnode.remove();
     expect(node.nodes.length, 2);
     expect(node.nodes[0], isText);
     expect(node.nodes[1], isComment);