refactor(angular.dart): remove undefined export

ShadowRootAware is defined in annotation.dart and not in annotation_src.dart.

Closes #1313

Author: BlackHC

lib/core/annotation.dart

@@ -8,7 +8,6 @@ import "dart:html" show ShadowRoot;
 export "package:angular/core/annotation_src.dart" show
     AttachAware,
     DetachAware,
-    ShadowRootAware,
 
     Formatter,
     DirectiveBinder,