Remove obsolete ready and error events from MediaKeySession.

Source/modules/encryptedmedia/MediaKeySession.idl

Index: Source/modules/encryptedmedia/MediaKeySession.idl
diff --git a/Source/modules/encryptedmedia/MediaKeySession.idl b/Source/modules/encryptedmedia/MediaKeySession.idl
index d81309d6d6085adb4521cc6f3a311a69d7d2b53a..379befa8ae94e73ee5711e4f2d3f6f22c34280d6 100644
--- a/Source/modules/encryptedmedia/MediaKeySession.idl
+++ b/Source/modules/encryptedmedia/MediaKeySession.idl
@@ -29,11 +29,7 @@
     GarbageCollected,
     TypeChecking=Interface
 ] interface MediaKeySession : EventTarget {
-    // error state
-    readonly attribute MediaKeyError error;
-
     // session properties
-    readonly attribute DOMString keySystem;
     readonly attribute DOMString sessionId;
     readonly attribute unrestricted double expiration;
     [CallWith=ScriptState] readonly attribute Promise closed;