Remove support for remaining deprecated features.

sdk/lib/_internal/compiler/implementation/diagnostic_listener.dart

Index: sdk/lib/_internal/compiler/implementation/diagnostic_listener.dart
diff --git a/sdk/lib/_internal/compiler/implementation/diagnostic_listener.dart b/sdk/lib/_internal/compiler/implementation/diagnostic_listener.dart
index 67d379222ddf3f95274f248975a47f53ea835abe..ca73463967135cbfab78e4ee0bdd38500f3ff10f 100644
--- a/sdk/lib/_internal/compiler/implementation/diagnostic_listener.dart
+++ b/sdk/lib/_internal/compiler/implementation/diagnostic_listener.dart
@@ -23,9 +23,6 @@ abstract class DiagnosticListener {
 
   void reportInfo(Spannable node, MessageKind errorCode, [Map arguments]);
 
-  /// Returns true if a diagnostic was emitted.
-  bool onDeprecatedFeature(Spannable span, String feature);
-
   // TODO(ahe): We should not expose this here.  Perhaps a
   // [SourceSpan] should implement [Spannable], and we should have a
   // way to construct a [SourceSpan] from a [Spannable] and an