Drop [LegacyInterfaceTypeChecking] for APIs that are not enabled by default

third_party/WebKit/Source/core/animation/AnimationTimeline.idl

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // http://www.w3.org/TR/web-animations/#the-animationtimeline-interface
 
 // TODO(dstockwell): This interface has several changes in the latest spec:
 // https://w3c.github.io/web-animations/#the-animationtimeline-interface
 
 [
     RuntimeEnabled=WebAnimationsAPI,
     GarbageCollected,
 ] interface AnimationTimeline {
     attribute double? currentTime;
     attribute double playbackRate;
-    [LegacyInterfaceTypeChecking] Animation play(AnimationEffectReadOnly source);
+    Animation play(AnimationEffectReadOnly source);
     sequence<Animation> getAnimations();
 };