Work around npm preprocess not supporting nested ifdefs

Overview.src.html

@@ -2297,13 +2297,14 @@ <h3 id="animation-effect-speed-control">Animation effect speed control</h3>
     This is because the <a>active duration</a> will be updated but the
     <a>local time</a> will not.
 
-<!-- @ifdef INCLUDE_GROUPS-->
+<!-- We'd like to conditionally exclude the following paragraph based on
+     INCLUDE_GROUPS but the npm preprocess module doesn't support nested
+     @ifdefs -->
     Furthermore, if other <a>animation effects</a> depend on the
     <a>animation effect</a>'s <a>active duration</a>, such as sibling
     <a>animation effect</a> in a <a>sequence effect</a>, they
     too may jump as a result of setting the <a>animation effect</a>'s <a
     lt="animation effect playback rate">playback rate</a>.
-<!-- @endif -->
 
     For runtime speed control the <a
     lt="animation playback rate">playback rate</a> of the
@@ -3188,7 +3189,7 @@ <h4 id="relationship-of-group-time-to-child-time">Relationship of group time to
 
 <!-- We'd like to conditionally exclude the following point based on
      INCLUDE_ANIMATION_NODE_PLAYBACKRATE but the npm preprocess module
-     seems to be buggy when you have nested @ifdefs -->
+     doesn't support nested @ifdefs -->
 *   Setting the <a lt="animation effect playback rate">playback
     rate</a> of a <a>group effect</a> will speed up or slow down all
     children.