Remove meaningless uses of [TypeChecking=Nullable]

Source/core/animation/Timing.idl

Index: Source/core/animation/Timing.idl
diff --git a/Source/core/animation/Timing.idl b/Source/core/animation/Timing.idl
index 49e93e1d61ff9e88a1be4074541ed78e8f0de0b7..1bb3198c61034c415503320bccd5377b8c66de40 100644
--- a/Source/core/animation/Timing.idl
+++ b/Source/core/animation/Timing.idl
@@ -21,7 +21,7 @@
     // FIXME: If the user calls animation.specified.duration = "" (empty string) then duration
     // gets set to 0 (This is correct behavior for IDL). Correct result is for duration to
     // be set to 'auto'.
-    [TypeChecking=Interface|Nullable, ImplementedAs=setDuration] setter double (DOMString name, double duration);
+    [TypeChecking=Interface, ImplementedAs=setDuration] setter double (DOMString name, double duration);
 
     attribute double playbackRate;
     attribute DOMString direction;