Remove support for PushSubscription.subscriptionId.

Source/core/frame/UseCounter.cpp

Index: Source/core/frame/UseCounter.cpp
diff --git a/Source/core/frame/UseCounter.cpp b/Source/core/frame/UseCounter.cpp
index abc31cf69c2753e1b1891109c9e00cedda221af2..60f2d02ebd602cd7d1a4cb49e1e53236f2c67774 100644
--- a/Source/core/frame/UseCounter.cpp
+++ b/Source/core/frame/UseCounter.cpp
@@ -890,9 +890,6 @@ String UseCounter::deprecationMessage(Feature feature)
     case EncryptedMediaInsecureOrigin:
         return "requestMediaKeySystemAccess() is deprecated on insecure origins in the specification. Support will be removed in the future. You should consider switching your application to a secure origin, such as HTTPS. See https://goo.gl/rStTGz for more details.";
 
-    case PushSubscriptionId:
-        return "'PushSubscription.subscriptionId' is deprecated and is now included in 'PushSubscription.endpoint'. It will be removed in Chrome 45, around August 2015.";
-
     case DocumentGetCSSCanvasContext:
         return "The -webkit-canvas CSS feature is deprecated. Please use a positioned <canvas> element instead.";