Deprecates AsyncProxy

Deprecated AsyncProxy due to lack of usage and very limited use cases.
Will be made available as third-party library.

Change-Id: I8295f44e00cf9c26b0fef024dbae93f7e1c9d83a

user/src/com/google/gwt/user/client/AsyncProxy.java

diff --git a/user/src/com/google/gwt/user/client/AsyncProxy.java b/user/src/com/google/gwt/user/client/AsyncProxy.java
index c06354e..c14ec07 100644
--- a/user/src/com/google/gwt/user/client/AsyncProxy.java
+++ b/user/src/com/google/gwt/user/client/AsyncProxy.java
@@ -87,7 +87,11 @@
  * 
  * @param <T> the type of interface that must be implemented by the derivative
  *          class.
+ *
+ * @deprecated AsyncProxy will no longer be part of the SDK with next release. Please
+ *             look for third party libraries if you still need to use it.
  */
+@Deprecated
 @AsyncProxy.DefaultValue()
 public interface AsyncProxy<T> {
   /*