Move the public method HttpDateTime.parse() into AndroidHttpClient.

See bug http://b/2553589

Change-Id: Ide3399c7c63daf9c0b8c18669076f2f4d6e9a876
diff --git a/preloaded-classes b/preloaded-classes
index 54c7303..8114562 100644
--- a/preloaded-classes
+++ b/preloaded-classes
@@ -313,7 +313,7 @@
 android.net.http.EventHandler
 android.net.http.Headers
 android.net.http.HttpsConnection
-android.net.http.HttpDateTime
+com.android.internal.http.HttpDateTime
 android.net.http.Request
 android.net.http.RequestQueue
 android.net.http.SslCertificate