bindings: Remove [EventConstructor] and [InitializedByEventConstructor]

Source/core/events/EventInit.idl

Index: Source/core/events/EventInit.idl
diff --git a/Source/core/events/EventInit.idl b/Source/core/events/EventInit.idl
index 6d522dad3f5a46f6006a7c1247f138a2f8d24172..f94cf4e817a5ec227fb8b20763e4d3c86d006af3 100644
--- a/Source/core/events/EventInit.idl
+++ b/Source/core/events/EventInit.idl
@@ -2,10 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-[
-    // FIXME: Remove ImplementedAs once we replace all EventInits.
-    ImplementedAs=EventInitDictionary,
-] dictionary EventInit {
+// https://dom.spec.whatwg.org/#interface-event
+
+dictionary EventInit {
     boolean bubbles = false;
     boolean cancelable = false;
 };