Remove some obsolete entries in Web Animations IDL

third_party/WebKit/LayoutTests/web-animations-api/effect-of-keyframeeffect-on-getComputedTiming.html

Index: third_party/WebKit/LayoutTests/web-animations-api/effect-of-keyframeeffect-on-getComputedTiming.html
diff --git a/third_party/WebKit/LayoutTests/web-animations-api/effect-of-keyframeeffect-on-getComputedTiming.html b/third_party/WebKit/LayoutTests/web-animations-api/effect-of-keyframeeffect-on-getComputedTiming.html
index dd4b79cd75e78400613a821042ce98c3ca5ed806..77d15b5d024bcc9967f36d98f28f1a6c88974e13 100644
--- a/third_party/WebKit/LayoutTests/web-animations-api/effect-of-keyframeeffect-on-getComputedTiming.html
+++ b/third_party/WebKit/LayoutTests/web-animations-api/effect-of-keyframeeffect-on-getComputedTiming.html
@@ -66,7 +66,7 @@ test(function() {
 
 test(function() {
   var timing = new KeyframeEffect(element, keyframes).timing;
-  for (var attr of ['delay', 'endDelay', 'iterationStart', 'playbackRate']) {
+  for (var attr of ['delay', 'endDelay', 'iterationStart']) {
     assert_throws(new TypeError, function() { timing[attr] = NaN; }, attr);
     assert_throws(new TypeError, function() { timing[attr] = Infinity; }, attr);
   }