[web-animations-1] Simplify the description of Animation.play

This restores the updated description of Animation.play() that was added
in da4b585 but reverted in
5253a66.

Author: birtles

web-animations-1/Overview.bs

@@ -4072,9 +4072,8 @@ interface Animation : EventTarget {
     </div>
 
 :   <dfn method for=Animation lt='play()'>void play()</dfn>
-::  Unpauses the animation and rewinds if it has finished playing using
-    the procedure to <a>play an animation</a> for this object
-    with the <var>auto-rewind</var> flag set to true.
+::  Begins or resumes playback of the animation by running the procedure to
+    [=play an animation=] passing true as the value of the |auto-rewind| flag.
 :   <dfn method for=Animation lt='pause()'>void pause()</dfn>
 ::  Suspends the playback of this animation by running the procedure to
     <a>pause an animation</a> for this object.