Editorial: make kind attributes consistent

Helps with #9832.

source

@@ -35017,9 +35017,7 @@ interface <dfn interface>HTMLTrackElement</dfn> : <span>HTMLElement</span> {
   does not <span data-x="represents">represent</span> anything on its own.</p>
 
   <p>The <dfn element-attr for="track"><code data-x="attr-track-kind">kind</code></dfn> attribute is
-  an <span>enumerated attribute</span>. The following table lists the keywords defined for this
-  attribute. The keyword given in the first cell of each row maps to the state given in the second
-  cell.</p>
+  an <span>enumerated attribute</span> with the following keywords and states:</p>
 
   <table>
    <thead>
@@ -35062,10 +35060,10 @@ interface <dfn interface>HTMLTrackElement</dfn> : <span>HTMLElement</span> {
      <td><dfn data-x="attr-track-kind-metadata">Metadata</dfn>
   </table>
 
-  <p>The attribute may be omitted. The <i data-x="missing value default">missing value default</i>
-  is the <span data-x="attr-track-kind-subtitles">subtitles</span> state. The <i
-  data-x="invalid value default">invalid value default</i> is the <span
-  data-x="attr-track-kind-metadata">metadata</span> state.</p>
+  <p>The <i data-x="missing value default">missing value default</i> is the <span
+  data-x="attr-track-kind-subtitles">subtitles</span> state. The <i data-x="invalid value
+  default">invalid value default</i> is the <span data-x="attr-track-kind-metadata">metadata</span>
+  state.</p>
 
   <p>The <dfn element-attr for="track"><code data-x="attr-track-src">src</code></dfn> attribute
   gives the <span>URL</span> of the text track data. The value must be a <span>valid non-empty URL