Remove LibValidator to allow assets-only pub packages (http://dartbug.com/15810).

sdk/lib/_internal/pub/lib/src/validator.dart

Index: sdk/lib/_internal/pub/lib/src/validator.dart
diff --git a/sdk/lib/_internal/pub/lib/src/validator.dart b/sdk/lib/_internal/pub/lib/src/validator.dart
index 640c54ff2d699a5e0b2acfde626ec7e97c1b73e2..e4480581022eec14d98cd3f288c3c7e6c29d54dd 100644
--- a/sdk/lib/_internal/pub/lib/src/validator.dart
+++ b/sdk/lib/_internal/pub/lib/src/validator.dart
@@ -13,7 +13,6 @@ import 'validator/compiled_dartdoc.dart';
 import 'validator/dependency.dart';
 import 'validator/dependency_override.dart';
 import 'validator/directory.dart';
-import 'validator/lib.dart';
 import 'validator/license.dart';
 import 'validator/name.dart';
 import 'validator/pubspec_field.dart';
@@ -51,7 +50,6 @@ abstract class Validator {
   static Future<Pair<List<String>, List<String>>> runAll(
       Entrypoint entrypoint, [Future<int> packageSize]) {
     var validators = [
-      new LibValidator(entrypoint),
       new LicenseValidator(entrypoint),
       new NameValidator(entrypoint),
       new PubspecFieldValidator(entrypoint),