Revert "style: Make the transitions code make sense again."

This reverts commit d6092fae27.

This change actually makes transitions start, and our code for stopping
transitions is just bogus, so we just keep re-starting them over and over, which
is not good.

components/style/animation.rs

@@ -345,8 +345,8 @@ impl PropertyAnimation {
 
         let property_animation = PropertyAnimation {
             property: animated_property,
-            timing_function,
-            duration,
+            timing_function: timing_function,
+            duration: duration,
         };
 
         if property_animation.does_animate() {