Remove support for PushSubscription.subscriptionId.

LayoutTests/http/tests/push_messaging/subscribe-success-in-document.html

Index: LayoutTests/http/tests/push_messaging/subscribe-success-in-document.html
diff --git a/LayoutTests/http/tests/push_messaging/subscribe-success-in-document.html b/LayoutTests/http/tests/push_messaging/subscribe-success-in-document.html
index 2c6d49a159b69a2a5b94441dd13291fc1e81a23e..29684f05f8507b6e5107aada4f0a7dabc046cbe9 100644
--- a/LayoutTests/http/tests/push_messaging/subscribe-success-in-document.html
+++ b/LayoutTests/http/tests/push_messaging/subscribe-success-in-document.html
@@ -26,16 +26,9 @@ async_test(function(test) {
             return swRegistration.pushManager.subscribe();
         })
         .then(function(pushSubscription) {
-            assert_will_be_idl_attribute(pushSubscription, 'subscriptionId');
-            assert_equals(typeof pushSubscription.subscriptionId, 'string');
-
             assert_will_be_idl_attribute(pushSubscription, 'endpoint');
             assert_equals(typeof pushSubscription.endpoint, 'string');
 
-            // The |subscriptionId| attribute is being deprecated, and its value
-            // is now the last part of the |endpoint| attribute.
-            assert_true(pushSubscription.endpoint.endsWith(pushSubscription.subscriptionId));
-
             try {
                 var endpointUrl = new URL(pushSubscription.endpoint);
             } catch(e) {